Physicochemical techniques for determining the composition of canine and feline uroliths: a literature review / Técnicas físico-químicas para determinação da composição de urólitos em caninos e felinos: uma revisão de literatura

ABSTRACT: Urinary lithiasis has been reported as a problem that affects humankind since ancient times and has been described in several animal species. The condition is a consequence of other diseases that may be present in the urinary system or related to other body disorders. The stone composition needs to be analyzed to identify the possible causes that led to the formation and development of uroliths. For this, several techniques are currently available, some of which are promptly accessible, while others are not. Thus, this literature review aimed to perform a brief introduction on urolithiasis, present the most used techniques in the analysis of the composition of canine and feline uroliths and point out the advantages and disadvantages of each technique.

RESUMO: A litíase urinária foi reportada como um problema que atinge a humanidade desde a antiguidade e já foi descrita em diversas espécies de animais. A doença é considerada consequência de outras enfermidades que podem estar presentes no sistema urinário, ou relacionados com outros distúrbios do organismo. Para identificar as possíveis causas que levaram à formação e desenvolvimento de urólitos é importante analisar a composição dos cálculos. Para isso, existem várias técnicas disponíveis atualmente, algumas de mais fácil acesso e outras, nem tanto. Dessa forma, objetiva-se com a presente revisão realizar uma breve introdução sobre a urolitíase e apresentar as técnicas mais utilizadas na análise da composição de urólitos, em caninos e felinos, bem como apontar as vantagens e desvantagens de cada uma das técnicas.

Influence of alumina air-abrasion for highly translucent partially stabilized zirconia on flexural strength, surface properties, and bond strength of resin cement

Abstract Objective This study aims to evaluate the influence of different air-abrasion pressures and subsequent heat treatment on the flexural strength, surface roughness, and crystallographic phases of highly translucent partially stabilized zirconia (Y-PSZ), and on the tensile bond strength of resin cement to Y-PSZ. Methodology Fully sintered zirconia specimens were ground with SiC paper (control) and/or air-abraded with 50 µm particles of alumina at 0.1, 0.15, 0.2, or 0.3 MPa or left as-sintered. After air-abrasion at 0.2 MPa (0.2AB), additional specimens were then heated to 1500°C, and held for one hour at this temperature (0.2AB+HT1h). Flexural strength and surface roughness were evaluated. Crystalline phase identification was also carried out using X-ray diffraction. Bonded zirconia specimens with self-adhesive resin cement were stored in distilled water at 37°C for 24 h, either with or without aging (thermal cycling 4-60°C/20000). Results were analyzed statistically by ANOVA and Tukey-Kramer tests. Results The flexural strength decreased with the increase in air-abrasion pressure, while in contrast, the surface roughness increased. The lowest flexural strength and the highest roughness value were found for the 0.2AB and 0.3AB groups, respectively. All groups contained cubic-, tetragonal ( t )-, and rhombohedral ( r )-ZrO2 phases with the exception of the as-sintered group. Upon increasing the air-abrasion pressure, the relative amount of the r -ZrO2 phase increased, with a significant amount of r -ZrO2 phase being detected for the 0.2AB and 0.3AB groups. The 0.2AB+HT1h group exhibited a similar flexural strength and t -ZrO2 phase content as the as-sintered group. However, the 0.2AB group showed a significantly higher tensile bond strength (p<0.05) than the 0.2AB+HT1h group before and after aging. Conclusion Micromechanical retention by alumina air-abrasion at 0.2 MPa, in combination with chemical bonding of a resin to highly translucent Y-PSZ using a MDP-containing resin cement may enable durable bonding.

Polybrominated diphenyl ethers with broad spectrum antibacterial activity from the Indonesian marine sponge Lamellodysidea herbacea

The marine sponge Lamellodysidea herbacea is one of the marine organisms containing unique organobromine molecules polybrominated diphenyl ethers (PBDEs) which have diverse biological activities. Compounds 1−4 have been successfully isolated and their structures were elucidated using nuclear magnetic resonance (NMR) spectroscopy, single-crystal x-ray diffraction, and comparison with data in literature. Compound 1, C12H6 O4 Br6 , was isolated in gram quantity (1.35 g) and elucidated as 2,3,4,5-tetrabromo-6-(3ʹ,5ʹ-dibromo-2ʹ-hydroxyphenoxy)phenol after NMR and X-ray analysis. Compound 1 takes a twist-like conformation with torsion angle ϕ1 = 27.7 (6)°; ϕ2 = 86.5 (5)°, while the angle of the ether bond is 117.5°. Compounds 2−4 were elucidated as 2,3,5-tribromo-6-(3ʹ,5ʹdibromo-2ʹ-hydroxyphenoxy)anisole, 2,3,5-tribromo-6-(3ʹ,5ʹ-dibromomethoxyphenoxy) phenol, 2,3,5-tribromo-6- (3ʹ,5ʹ-hydroxyphenoxy)phenol, respectively. Antibacterial evaluation of 1−4 on Gram-positive and Gram-negative pathogens showed that the potent activity was at 0.08 µg/disk, 12 ± 0 mm (Staphylococcus aureus ATCC 6538); 6.25 µg/disk, 10 ± 0 mm (Klebsiella pneumoniae); and 50 µg/disk, 12 ± 0 mm (ampicillin-resistant Escherichia coli). Compounds 1, 2, and 4 showed ichthyotoxicity (zebrafish embryos, Danio rerio) at a level of LC50 >10 µg/ml [dead, 48 hours postfertilization (hpf)]. This is the first report that compound 4 inhibits the growth of antibiotic-resistant bacteria.

Discovery of a series of dimethoxybenzene FGFR inhibitors with 5pyrrolo2,3-pyrazine scaffold: structure-activity relationship, crystal structural characterization and study

Genomic alterations are commonly found in the signaling pathways of fibroblast growth factor receptors (FGFRs). Although there is no selective FGFR inhibitors in market, several promising inhibitors have been investigated in clinical trials, and showed encouraging efficacies in patients. By designing a hybrid between the FGFR-selectivity-enhancing motif dimethoxybenzene group and our previously identified novel scaffold, we discovered a new series of potent FGFR inhibitors, with the best one showing sub-nanomolar enzymatic activity. After several round of optimization and with the solved crystal structure, detailed structure-activity relationship was elaborated. Together with metabolic stability tests and pharmacokinetic profiling, a representative compound () was selected and tested in xenograft mouse model, and the result demonstrated that inhibitor was effective against tumors with FGFR genetic alterations, exhibiting potential for further development.

Comparación de la eficacia de la α-microglobulina-1 placentaria vs cristalografía en factores que modifican el resultado / Effectiveness comparison of α-microglobulin-1 placentary vs crystallography in the presence of factors that modify the result

Resumen Objetivo: Comparar la eficacia de la prueba α-microglobulina-1 placentaria (AmniSure®) versus cristalografía como método diagnóstico de ruptura de membranas en situaciones clínicas que modifican el resultado debido al gel lubricante, vaginosis bacteriana, sangre y escurrimiento genital anormal. Materiales y métodos: Estudio prospectivo, cuasi experimental y exploratorio, efectuado en pacientes embarazadas atendidas en el Hospital General de México, por sospecha de ruptura prematura de membranas. Criterios de inclusión: sospecha de ruptura prematura de membranas, independientemente de las semanas de embarazo, ruptura de membranas acompañada de sangrado, cervicovaginitis, hidrorrea o corioamnioitis; haber sido exploradas con gel lubricante y referir salida de líquido transvaginal. Resultados: Se efectuaron 20 pruebas con α-microglobulina-1 placentaria a la par de 20 cristalografías. Se descartó una prueba de α-microglobulina-1 por mala técnica de uso; se encontró una sensibilidad de 85.7% y especificidad de 100%. La sensibilidad de las cristalografías fue de 78.5% y especificidad de 100%. Conclusiones: Al comparar la efectividad de la α-microglobulina-1 placentaria versus la cristalografía se encontró mayor sensibilidad con la primera. Por tanto, es un método con mayor efectividad para detectar ruptura de membranas, independientemente de la edad gestacional o la coexistencia de factores que modifican el resultado. Ambas pruebas reportaron 100% de especificidad.

Abstract Objective: To compare the efficacy of the α-microglobulin-1 placental test (AmniSure®) against crystallography as a diagnostic method for premature rupture of membranes in clinical situations involving impaired outcome such as lubricating gel, bacterial vaginosis, blood and abnormal genital drainage. Materials and methods: A prospective, quasi- experimental and exploratory study was performed on 20 patients admitted to the Hospital General de México, who presented suspicion of premature rupture of membranes (PRM) and met the inclusion criteria: pregnant patients who presented suspicion of PRM, regardless of gestational age, patients with PRM accompanied by bleeding, cervicovaginitis, hydrorrhea and chorioamnioitis, who were reviewed with lubricating gel as well as those who referred transvaginal fluid outflow. Results: Twenty tests were performed with AmniSure® in addition to 20 crystallographies. An Amnisure test was discarded for poor technique of use, finding a sensitivity of 85.7% with a specificity of 100% and in the case of crystallography, the sensitivity was 78.57%, with a specificity of 100% Conclusions: When comparing the effectiveness of AmniSure® with crystallography for the diagnosis of PRM in the presence of factors that can modify the result, 7.2% greater Amnisure sensitivity was found on crystallography and both tests showed 100% specificity.

Rational design of GRK2 inhibitors for the treatment of heart failure / 中国药理学与毒理学杂志

G protein-coupled receptors (GPCRs) convert extracellular stimuli in the form of hormones, odorants and light into profound changes in cell homeostasis. Their timely desensitization is critical for cells to rapidly respond to changes in their environment and to avoid damage from sustained signaling. Seven GPCR kinases (GRKs) phosphorylate and regulate the activity of most of the ~800 GPCRs in the human genome. Although GRKs normally play an adaptive role, in conditions such as chronic heart failure they are overexpressed and linked to disease progression. GRK2 and GRK5 have thus become important targets for the treatment of heart failure and pathological cardiac hypertrophy, respectively. Our lab has determined atomic structures representing all three vertebrate GRK subfamilies, and is now in the midst of a campaign to develop selective inhibitors of these enzymes using structure-based rational design. We have identified the FDA approved drug paroxetine as a selective GRK2 inhibitor, determined the crystal structure of the GRK2·paroxetine complex and, in collaboration with the Koch lab, showed that the drug improves contractility in myocytes and, most impressively, recovery in post-myocardial infarcted mice. Since then, we have identified additional chemical scaffolds that exhibit even higher potency and/or selectivity for GRK5. Using a ″hybrid″ inhibitor design approach we have generated GRK selective chemical probes that exhibit improved potency and stability and are able to increase inotropy and dampen the hypertrophic response in cardiomyocytes and small animal models. Structural analysis has revealed the molecular basis for selectivity and potency in many of these compounds, allowing for the design of future generations of GRK chemical probes.

Studies on sesquiterpene lactones from Carpesium faberi / 中国中药杂志

By using various chromatographic techniques,18 sesquiterpene lactones were isolated from the acetone extract of Carpesium faberi. Their structures were identified on the basis of comprehensive spectroscopic data, involving 2 carabrane sesquiterpenoids [carabrone(1), 4R-carabrol(2)], 3 eudesmane sesquiterpenoids [granilin(3), 3-epi-isotelekin(4), 1α-hydroxypinatifidin(5)], 8 guaiane sesquiterpenoids [4β,10α-dihydroxy-5α(H)-1,11(13)-guaidien-8α,12-olide(6), 8-epi-helenium lactone(7), 4-epi-isoinuviscolide(8), 9β,10β-epoxy-4α-hydroxy-1β-H,11α-H-guaian-8α,12-olide(9), 4α,10α-dihydroxy-1β(H),5β(H)-guaian-11-(13)-en-8α,12-olide(10), 4α-hydroxy-9β,10β-epoxy-11β-H,5α-H-guaian-11(13)-en-8α,12-olide(11), 4α-hydroxy-1β,5α,11α-H-guaian-9(10)-en-8α,12-olide(12), inuviscolide(13)], 1 pseudoguaiane sesquiterpenoid [(+)-confertin(14)], 3 germacrane sesquiterpenoids [madolin B(15), carabrolactone A(16),11(13)-dehydroivaxillin(17)], 1 xanthane sesquiterpenoid [tomentosin(18)]. Furthermore, the absolute configuration of 1 was confirmed by Cu-Kα X-ray crystallographic analysis,and the R-configuration of the chiral center at C-4 in 2 was established by the modified Mosher's method.The compounds 2-5, 7 and 9-15 were isolated from this plant for the first time, and compounds 4-5, 7, and 12-15 were isolated from this genus for the first time.In addition, the neurotrophic activity of compounds 1-3, 6 and 17 were evaluated by morphological observation and statistical analysis of cells differentiation, using rat pheochromocytoma(PC12)cells as a model system. However, all compounds were inactive.

In Silico Inhibitory Activity against Caspase 3 by Zinc (II) Coordinated Complexes.

Aims: The presented research paper is aimed to prevalence of apoptosis for the first time by using in silico molecular docking and simulation using caspase-3 zymogen and zinc-coordinated compounds. Antioxidant activities of the coordinated complexes were compared to the positive controls (BHT and ascorbic acid). Study design: Molecular docking analysis was performed by using Autodock 4.2, setting at 150x140x110 Gridbox, center at -57.616, 31.092, 88.666 with 0.375 Å spacing. Their antioxidant activity was tested by FRAP and DPPH assay. Place and Duration of Study: Department of Chemistry and department of molecular medicine, Faculty of Medicine, University of Malaya laboratories between January 2014 – July 2014 Methodology: Compounds derived from zinc(II) ion give rise to coordination complexes exhibited CHN, NMR (1H & 13C) and FT-IR spectra consistent with the proposed structures. Based on the x-ray crystal structure, one of the derivatives is a mononuclear square-pyramidal metal complex, with τ value of 0.35. The molecular docking simulation formed between compounds and caspase 3 showed the ligands bind to the active-site gorge well positioned in the active-site gorge. Results: The residues that have been involved in this protein-ligand interaction docked well by using Autodock 4.2, setting at 150x140x110 Gridbox, center at -57.616, 31.092, 88.666 with 0.375 Å spacing in the hydrophobic pocket. Their antioxidant activity tested revealed their FRAP assay values of 531.11±0.021 and 1886.11±0.008 higher than value of 187.3±2.6 shown by BHT used as standard. The compounds showed IC50 values 21.50±0.009 and 14.80±0.002 lower than ascorbic acid with an IC50 value of 2.26±0.001 μg/mL. Conclusion: Synthesized zinc(II) complexes have been confirmed to inhibit the activity of caspase 3 both in silico and in vitro and were tested for antioxidant activity by both FRAP and DPPH methods.

Polimorfismo na produção de medicamentos / Polymorphism in the manufacture of medicines

O polimorfismo pode ocasionar desvios de qualidade durante o processo produtivo e influenciar o desempenho dos medicamentos. Por isso, o entendimento do fenômeno e suas implicações abre um campo amplo de possibilidades a serem exploradas na área farmacêutica, incluindo o surgimento de novos paradigmas e ferramentas na garantia da qualidade de medicamentos. Este trabalho apresenta uma introdução aos aspectos básicos do fenômeno do polimorfismo e suas implicações na produção e controle de medicamentos, com ênfase no polimorfismo dos fármacos.

Polymorphism can cause quality deviations during the production of medicines and can influence their effectiveness. Therefore, an understanding of this phenomenon and its implications opens a wide of possibilities to be explored in the pharmaceutical , including the emergence of new paradigms and tools for the quality assurance of medicines. This paper presents an introduction to basic aspects of the polymorphism phenomenon and its implications for the production and control of medicines, with emphasis on drug polymorphs.

Crystal structure of Vibrio cholerae HutX protein / 第二军医大学学报

Objective To obtain purified Vibrio cholerae HutX and its diffraction data. Methods Protein HutX was obtained by gene cloning and protein expression, purified by nickcl sepharose affinity chromatography, anion exchange chromatography (source Q), and molecular sieve chromatography (Superdex 200), and identified by Western blotting analysis. Then the obtained protein was subjected to crystallization condition screening and hanging drop optimization. The obtained crystal structure was analyzed by X-ray diffraction method. Results Western blotting analysis indirectly indicated that the obtained protein was HutX protein. Then the HutX crystal and its diffraction data were obtained in the present study. Conclusion The findings of the present study pave a way for future research on the crystal structure and function of HutX protein and its role in heme utilization of Vibrio cholerae.

Preparation, Crystallization and Preliminary X-ray Crystallographic Analysis of Smu.776 From Caries Pathogen Streptococcus mutans / 生物化学与生物物理进展

The gene smu. 776 encodes a possible S-adenosylmethionine-dependent methyltransferase of 385 residues in Streptococcus mutans, a primary pathogen for human dental caries. The DNA fragment of smu.776 was cloned into pET28a and expressed in good amount from the E. coli strain BL21 (DE3). Smu.776 protein was purified to homogeneity in a two-step procedure ofNi2+ chelating and size exclusion chromatography. Crystals were obtained by hanging-drop vapor diffusion method and diffracted to 2.0 (A) resolution.The crystal belongs to orthorhombic space group C2 with cell dimension of a=168.47 (A), b= 50.66 (A), c=53.96 (A), β=104.22°. The asymmetric unit is expected to contain one molecule with solvent content of 51.3%.

New Progress in Function and Structure of The Class Ⅰ Polypeptide Release Factors / 生物化学与生物物理进展

The process of protein synthesis is terminated by one of the three stop codons which are recognized by classⅠ polypeptide release factors.Subsequently, it could promote the hydrolysis of the ester bond of peptidy-tRNA, resulting in release of the nascent polypeptide.Recent results from cryoelectron microscopy, crystallography, NMR, molecular dynamic and biochemical experiments have shed considerable light on the function and structure of the classⅠ release factors.The progress in these aspects were summarized.

Protein Preparation, Crystallization and Preliminary X-ray Crystallographic Analysis of Smu.260 From Streptococcus mutans--a Cariogenic Dental Pathogen / 生物化学与生物物理进展

Smu. 260 encodes a putative protein of 200 residues in Streptococcus mutans, a primary pathogen for human dental caries. Smu. 260 was cloned into expression vector pET28a and expressed in good amount trom the E. coli strain BL21 (DE3). Smu.260 protein was purified to homogeneity in a two-step procedure of Ni2+ chelating and size exclusion chromatography. The purified protein exists in two forms, a dimer form about 46 ku with yellow color and a tetramer form without apparent color. Crystals were obtained from the dimer protein by hanging-drop vapor-diffusion method. The crystals diffracted to about 2.3 A resolution and belong to orthorhombic space group P212121 with cell dimensions of a = 89.88A, b = 90.91 A, c = 105.17 A. The asymmetric unit is expected to contain two dimers with solvent content of 53%.

Crystallography, morphology, and thermal properties of starch in Fritillaria thunbergii and F. ussurensis as well as comparison with potato starch / 中草药

Objective To fully understand the medicinal plants of Fritillaria L. , the physicochemical properties of starch in two species of Fritillaria L. , F. thunbergii and F. ussurensis. were investigated by means of various analytical methods. Methods The properties of starch in the two different species of Fritillaria L. were compared by X-ray diffraction, scanning electron microscope (SEM) and themogravimetric analysis (TGA). Results The crystal type of starch in the two species of Fritillaria L.was the characteristic B-type which was in consistent with that of potato starch. The degrees of crystallinity of F. thunbergii starch and F. ussurensis starch were about 29.9% and 20.1%, respectively. However,the degree of crystallinity of the potato starch was 44.9%. From the crystallinity degree of the starch in two species of Fritillaria L. , it could be concluded that the content of amylose in F. ussurensis starch was higher than that in F. thunbergii starch. The granule size of the starch in two species of Fritillaria L.ranged from 5 to 40 μm, which were all smaller than that of the potato. The starch granule in two species of Fritillaria L. was in cycloidal or elliptic-shape. It could be concluded that the thermal stability of the starch in two species of Fritillaria L. was different due to the different structures of different starch in various plants by TGA. Conclusion The physicochemical properties of starch in two different species of Fritillaria L. differ a lot due to their geographical origin.

A model for the reaction mechanism of the transglutaminase 3 enzyme

Transglutaminase enzymes (TGases) catalyze the calcium dependent formation of an isopeptide bond between protein-bound glutamine and lysine substrates. Previously we have shown that activated TGase 3 acquires two additional calcium ions at site two and three. The calcium ion at site three results in the opening of a channel. At this site, the channel opening and closing could modulate, depending on which metal is bound. Here we propose that the front of the channel could be used by the two substrates for enzyme reaction. We propose that the glutamine substrate is directed from Trp236 into the enzyme, shown by molecular docking. Then a lysine substrate approaches the opened active site to engage Trp327, leading to formation of the isopeptide bond. Further, direct comparisons of the structures of TGase 3 with other TGases have allowed us to identify several residues that might potentially be involved in generic and specific recognition of the glutamine and lysine substrates.

Structural basis for inhibition of protein tyrosine phosphatases by Keggin compounds phosphomolybdate and phosphotungstate

Protein-tyrosine phosphatases (PTPs) constitute a family of receptor-like, and cytoplasmic enzymes, which catalyze the dephosphorylation of phosphotyrosine residues in a variety of receptors and signaling molecules. Together with protein tyrosine kinases (PTKs), PTPs are critically involved in regulating many cellular signaling processes. In this study, diverse compounds were screened for PTP inhibition and selectively screened for inhibitors with the end product inhibition properties. Among phosphate analogues and their derivatives for PTP inhibition, Keggin compounds phosphomolybdate (PM) and phosphotungstate (PT) strongly inhibited both PTP-1B and SHP-1, with K(i) values of 0.06-1.2 micromM in the presence of EDTA. Unlike the vanadium compounds, inhibition potencies of PM and PT were not significantly affected by EDTA. PM and PT were potent, competitive inhibitors for PTPs, but relatively poor inhibitors of Ser/Thr phosphatase. Interestingly, PM and PT did not inhibit alkaline phosphatase at all. The crystal structure of PTP-1B in complex with PM, at 2.0 A resolution, reveals that MoO(3), derived from PM by hydrolysis, binds at the active site. The molybdenium atom of the inhibitor is coordinated with six ligands: three oxo-ligands, two apical water molecules and a S atom of the catalytic cysteine residue. In support of the crystallographic finding, we observed that molybdenium oxides (MoO(3), MoO(2), and MoO(2)Cl(2)) inhibited PTP-1B with IC(50) in the range 5-15 micromM.

Crystallography,morphology,and thermal properties of starch in Fritillaria thunbergii and F.ussurensis as well as comparison with potato starch / 中草药

Objective To fully understand the medicinal plants of Fritillaria L.,the physicochemical properties of starch in two species of Fritillaria L.,F.thunbergii and F.ussurensis.were investigated by means of various analytical methods.Methods The properties of starch in the two different species of Fritillaria L.were compared by X-ray diffraction,scanning electron microscope(SEM) and themogravimetric analysis(TGA).Results The crystal type of starch in the two species of Fritillaria L.was the characteristic B-type which was in consistent with that of potato starch.The degrees of crystallinity of F.thunbergii starch and F.ussurensis starch were about 29.9% and 20.1%,respectively.However,the degree of crystallinity of the potato starch was 44.9%.From the crystallinity degree of the starch in two species of Fritillaria L.,it could be concluded that the content of amylose in F.ussurensis starch was higher than that in F.thunbergii starch.The granule size of the starch in two species of Fritillaria L.ranged from 5 to 40 ?m,which were all smaller than that of the potato.The starch granule in two species of Fritillaria L.was in cycloidal or elliptic-shape.It could be concluded that the thermal stability of the starch in two species of Fritillaria L.was different due to the different structures of different starch in various plants by TGA.Conclusion The physicochemical properties of starch in two different species of Fritillaria L.differ a lot due to their geographical origin.

The magnesium protein interaction in nucleotide complexes of phosphoglycerate kinase.

The X-ray structure determination of yeast phosphoglycerate kinase and subsequent substrate binding studies have helped to define the binding sites for the triose and nucleoside phosphate substrates. This communication deals with one feature of the binding site—the location of an aspartic acid residue close to the phosphoryl binding site of the nucleotide substrate—and relates this and other structural features of the active site to the properties of this enzyme as deduced from nuclear magnetic resonance studies.

Spatial organization of catalase proteins.

The three-dimensional structure of the heme-containing fungal catalase from Penicillium vitale (m.m. 2,80,000) has been studied by X-ray analysis at 2·0 A resolution. The molecule is tetramer, each subunit contains 670 aminoacid residues identified to construct “X-ray” primary structure. The subunit is built of three compact domains and their connections. The first domain of about 350 residues contains a β-barrel flanked by helices, the second domain of 70 residues is formed by four helices and the third one is composed of 150 residues and is topologically similar to flavodoxin. The active site including heme is deeply buried near the β-barrel. A comparison of the structure of catalase from Penicillium vitale with that of beef liver catalase revealed very close structural homology of the first and the second domain, but the third domain is entirely absent in beef liver catalase. A catalase from thermophillic bacteria Thermus thermophilus (m.m. 2,10,000) has been first isolated, crystallized and studied by X-ray analysis. Crystals are cubic, space group is P213, a = 133·4 Å. The molecule is a hexamer with trigonal symmetry 32. The electron density map at 3 Å resolution made it possible to trace the polypeptide chain. The main structural motif is formed by four near parallel helices. There is no heme in Thermus thermophilus catalase, the active site is between the four helices and contains two manganese ions.

Structural mobility and transformations in globular proteins.

Although globular proteins are endowed with well defined three-dimensional structures, they exhibit substantial mobility within the framework of the given threedimensional structure. The different types of mobility found in proteins by and large correspond to the different levels of organisational hierarchy in protein architecture. They are of considerable structural and functional significance, and can be broadly classified into (a) thermal and conformational fluctuations, (b) segmental mobility, (c) interdomain mobility and (d) intersubunit mobility. Protein crystallographic studies has provided a wealth of information on all of them. The temperature factors derived from X-ray diffraction studies provide a measure of atomic displacements caused by thermal and conformational fluctuations. The variation of displacement along the polypeptide chain have provided functionally significant information on the flexibility of different regions of the molecule in proteins such as myoglobin, lysozyme and prealbumin. Segmental mobility often involves the movement of a region or a segment of a molecule with respect to the rest, as in the transition between the apo and the holo structures of lactate dehydrogenase. It may also involve rigidification of a disordered region of the molecule as in the activation of the zymogens of serine proteases. Transitions between the apo and the holo structures of alcohol dehydrogenase, and between the free and the sugar bound forms of hexokinase, are good examples of interdomain mobility caused by hinge-bending. The capability of different domains to move semi-independently contributes greatly to the versatility of immunoglobulin molecules. Interdomain mobility in citrate synthase appears to be more complex and its study has led to an alternative description of domain closure. The classical and the most thoroughly studied case of intersubunit mobility is that in haemoglobin. The stereochemical mechanism of the action of this allosteric protein clearly brings out the functional subtilities that could be achieved through intersubunit movements. In addition to ligand binding and activation, environmental changes also often cause structural transformations. The reversible transformation between 2 Zn insulin and 4 Zn insulin is caused by changes in the ionic strength of the medium. Adenylate Kinase provides a good example for functionally significant reversible conformational transitions induced by variation in pH. Available evidences indicate that reversible structural transformations in proteins could also be caused by changes in the aqueous environment, including those in the amount of water surrounding protein molecules.