Some physico-chemical and thermodynamic characteristics of maize starches hydrolyzed by glucoamylase.

Glucoamylolysis of maize starch at 55 °C has been studied by means of scanning electron microscopy (SEM), wide-angle X-ray diffraction spectroscopy (WAXD), and differential scanning calorimetry (DSC). It was found that hydrolysis is accompanied by changes in thermodynamic parameters of diluted aqueous dispersions of partially hydrolyzed starches. Such changes are ensured by two processes directly from hydrolysis and accompanying annealing. At relatively low degrees of hydrolysis (less than 30%), changes in thermodynamic parameters are mainly controlled by annealing. At the same time, at high degrees of hydrolysis (more than 40%), the main contribution to changes in thermodynamic parameters of partially hydrolyzed starch granules is due to the hydrolysis itself. It has been established that the main controlling parameter is the thickness of crystalline lamellae Lcrl, which, when annealed, increases, but tends to decrease at deeper glucoamylolisis. It has been established that the thickness Lcrl of crystalline lamellae, which increases with annealing, but shows a tendency to decrease with deeper glucoamylolysis is the most representative parameter of changes in maize starch after hydrolysis.

Study of α-crystallin structure by small angle neutron scattering with contrast variation.

The structure of the oligomeric protein α-crystallin from bovine eye lens was investigated by small-angle neutron scattering (SANS) with contrast variation. Based on the SANS curves, the match point for α-crystallin (43% D2O) and its average scattering length density at this point (2.4·10(10) cm(-2)) were evaluated. The radius of gyration and the distance distribution functions for α-crystallin were calculated. On the basis of these calculations, it was concluded that α-crystallin is characterized by homogeneous distribution of scattering density in the domains inaccessible for water penetration, and all polypeptide subunits in α-crystallin oligomers undergo equal deuteration. The latter indicates that all α-crystallin subunits are equally accessible for water and presumably for some other low molecular weight substances. These conclusions on the α-crystallin structure (homogeneous distribution of scattering density and equal accessibility of all subunits for low molecular weight substances) should be taken into account when elaborating α-crystallin quaternary structure models.

[Heat-induced structural transition of alpha-crystallin in the eye lens tissue observed by small-angle X-ray scattering].

Heat-induced structural transitions of crystallins in the eye lens tissue have been studied by small-angle X-ray scattering. It was shown that a short-time (approximately 1 min) incubation of the bovine eye lens tissue at a temperature of about 60 degrees C leads to a pronounced shift of the small-angle X-ray diffraction maximum due to the short-range order of alpha-crystallin oligomers. This shift indicates an increase in the molecular mass of alpha-crystallin oligomers. The results are evidence that, in the native surrounding and at the native concentration of alpha-crystallin, heat-induced transition of alpha-crystallin quaternary structure takes place. Earlier, this transition of alpha-crystallin has been observed only in solutions and gels of this protein. The results confirm the identity of alpha-crystallin properties in vitro and in vivo.

Resistance of alpha-crystallin quaternary structure to UV irradiation.

The damaging effect of UV radiation (lambda > 260 nm) on bovine alpha-crystallin in solution was studied by small-angle X-ray scattering, gel permeation chromatography, electrophoresis, absorption and fluorescence spectroscopy, and differential scanning calorimetry. The results obtained show that damage to even a large number of subunits within an alpha-crystallin oligomer does not cause significant rearrangement of its quaternary structure, aggregation of oligomers, or the loss of their solubility. Due to the high resistance of its quaternary structure, alpha-crystallin is able to prevent aggregation of destabilized proteins (especially of gamma- and beta-crystallins) and so to maintain lens transparency throughout the life of an animal (the chaperone-like function of alpha-crystallin).

[Studies of alpha- and betaL-crystallin complex formation in solution at 60 degrees C]. / Issledovanie kompleksoobrazovaniia v rastvorakh alpha-betaL-kristallinov pri 60 C.

Studies of molecular mechanisms of chaperone-like activity of alpha-crystallin became an active field of research over last years. However, fine interactions between alpha-crystallin and the damaged protein and their complex organization remain largely uncovered. Complexation between alpha- and betaL-crystallins was studied with thermal denaturation of betaL-crystallin at 60 degrees C using small-angle X-ray scattering (SAXS), light scattering, gel-permeation chromatography and electrophoresis. A mixed solution of alpha- and betaL-crystallins in concentrations about 10 mg/ml incubated at 60 degrees C was found to contain their soluble complexes with mean radius of gyration approximately 14 nm, mean molecular weight approximately 4000 kDA and maximal size approximately 40 nm. In pure betaL-crystallin solution, complexes were not observed at 60 degrees C. In SAXS studies, transitions in the alpha-crystallin quaternary structure at 60 degrees C were shown to occur and result in a double increase of the molecular weight. It suggests that during the temperature-induced denaturation of betaL-crystallin it binds with modified alpha-crystallin or, alternatively, alpha-betaL-crystallin complexation and alpha-crystallin modifications are concurrent. Estimates of the alpha-betaL-crystallin dimensions and relative contents of alpha- and betaL-crystallins in the complex suggest that several alpha-crystallin molecules are involved in complex formation.

[Comparative study of the crystallin supramolecular structure in the carp, frog, and rat lenses by small-angle roentgen ray scattering]. / Sravnitel'noe issledovanie nadmolekuliarnoi struktury kristallinov v khrustalikakh karpa, liagushki i krysy metodom malouglovogo rasseianiia rentgenovskikh luchei.

The supramolecular structure of crystallins in intact ocular lenses of carp, frog and rat as well as in the interior (nuclear) and outer (cortical) parts of these lenses was studied by the small-angle X-ray scattering method. The results show that the supramolecular structure of crystallins substantially varies both in lenses of different vertebrate species and in various parts of the same lens. In carp lens and in the cortical part of rat lens, crystallins have an ordered supramolecular structure, as indicated by a small-angle X-ray diffraction maximum in the region of Bragg distances 15-20 nm, whereas in frog lens and in the nuclear part of rat lens, the supramolecular structure of these proteins is disordered. The power-law X-ray scattering by rat lens nucleus may be evidence of fractal structures in the lens. A comparison of these results with literary data indicates that there is no obvious correlation between the type of supramolecular structure of crystallins and their polypeptide composition in lenses of different vertebrate species. The results suggest that the supramolecular ordering (short-range order) of crystallins is not a necessary condition for lens transparency.

[On the supramolecular structure of eye lens crystalline. A study by small-angle x-ray scattering]. / O nadmolekuliarnoi strukture kristallinov v khrustalike glaza. Issledovanie metodom rentgenovskogo malouglovogo rasseianiia.

The supramolecular structure of clystallins from bovine and frog eye lens tissues was studied by small-angle X-ray scattering. The measurements were carried out at different orientations of the lens tissue on a diffractometer equipped with a coordinate detector with point collimation of the X-ray beam. The results indicate that crystallins occur in the lens in different structural states. One state is characterized by a small-angle diffraction maximum in the range of Bragg's distances D-15-22 nm, which is explained by a near order of macromolecular complexes of crystallins (alpha-crystallin), whereas for the other state, small-angle diffraction maxima in the range D-15-22 nm are not observed. The assumption is made that the second state is related to a homogeneous distribution of crystallin polypeptides in the lens and that the transition from this state to the state with the near order of macromolecular complexes may be due to the chaperone activity of these proteins.

[Photoreceptor membrane assymetric structure in separated phase state]. / Asimmetrichnaia struktura fotoretseptorno'i membrany v sostoianii fazovogo razdeleniia.

The structure of unbleached bovine retinal rod photoreceptor membranes isolated in ficoli density gradient has been studied by means of small-angle X-ray diffraction methods. Samples were prepared in the form of thin multilamellar films of photoreceptor membranes in phase-separated state induced by partial dehydration. Diffraction data were collected using diffractometer with linear position-sensitive detector. Phase signs of structure amplitude were determined by method [7] and membrane lamellar electron density distribution was calculated at 1, 7 nm resolution. The results obtained showed photoreceptor membranes isolated in ficoli density gradient to have asymmetric structure which differed from that of photoreceptor membranes isolated in sucrose density gradient [1]. The asymmetry observed may be accounted for different content of lipid L alpha and L beta phases in cytoplasmic and intradisk membrane layers. It may be assumed that ficoli helps to support membrane native structure.

[X-ray structural study of the effect of light on isolated bovine photoreceptor membranes]. / Rentgenostrukturnoe issledovanie vozdeistviia sveta na izolirovannykh fotoretseptornye membrany byka.

The structure of multilamellar films prepared by air-drying of bovine retinal rod photoreceptor membrane suspension has been studied by means of small-angle X-ray diffraction methods. No reliable photoreceptor membrane structure modifications were observed with 100 s temporal resolution after the illumination of the film consisting of dark-adopted membranes. The comparative study of air-dried films prepared from dark-adopted and bleached photoreceptor membranes revealed no difference in their structures too. The structure alterations of photoreceptor membranes were recorded in the case of high (damaging) doses of visible light acting on photoreceptor membranes in suspension.

[Absence of small-angle maximums on the x-ray images of ocular lens tissue]. / Otsutstvie malouglovykh maksimumov na rentgenogrammakh tkani khrustalika glaza.

X-ray small-angle scattering study of bovine lens tissue was carried out. It was shown that X-ray patterns of lens cortical and nuclear native tissues did not contain the small-angle maxima. The maximum in the range of 15-20 nm Bragg distance appeared as a result of the lens tissue partial dehydration. Earlier such maximum was considered by some authors as the evidence of crystallin proteins short-range order in the native lens. Now it is confirmed to be a preparative artefact of dehydration. It was shown also that similar maximum in 15-20 range existed in the case of concentrated crystallin solutions. This indicates that supramolecular organization of crystallins in the native lens is not similar to that in the concentrated solution.

Structural conversions of crystallins under senile cataract, dehydration and UV-irradiation studied by X-ray diffraction.

By means of X-ray diffraction analysis, structural conversions of crystallins in human lens were detected in senile cataract and upon artificial dehydration of lens tissue. In senile cataract certain characteristics of the native three-dimensional structure of gamma- and beta-crystallins are completely lost, whereas during dehydration of lens tissue a small but significant contraction of these protein molecules takes place. Upon artificial UV-irradiation of bovine crystallins destructive changes are observed, which are very similar to those in cataract.

[A structural study of crystallins in the normal and cataractous crystalline lens by x-ray diffraction]. / Strukturnoe issledovanie kristallinov v normal'nom i kataraktal'nom khrustalike metodom difraktsii rentgenovskikh luchei.

Nucleus of the normal and cataractous human lenses were studied by means of the X-ray diffraction method. The conformational changes, as it is shown, take place during cataract formation. The similar as in senile cataract, conformational changes of bovine lens crystallins were induced by UV irradiation.

[Comparative study of crystallins from the nucleus and cortex of the bovine ocular lens by the gel filtration and x-ray diffraction methods]. / Sravnitel'noe issledovanie kristallinov iadra i korteksa glaza byka metodami gel'-filtratsii i difraktsii rentgenovskikh luchei.

Water--soluble proteins (alpha-, beta H-, beta L- and gamma-crystallins) from the bovine lens nucleus and cortex were fractionated and compared by gel filtration on Sephadex G-200. X-ray diffraction patterns from concentrated gels of these proteins were obtained. It allowed to compare qualitatively the structures of different crystallins and also to identify the maxima on X-ray diffraction patterns of the lens intact tissue.

[Comparative study of bovine ocular lens proteins in native tissue and an extract using the x-ray diffraction method]. / Sravnitel'noe issledovanie belkov khrustalika glaza byka v nativnoi tkani i v ékstrakte metodom difraktsii rentgenovskikh luchei.

It has been shown that the maxima (Bragg-spacings 4,5-19 A) on the X-ray diffraction patterns of the bovine lens native tissues from nuclear and cortical parts are predominantly due to the water-soluble crystallin intramolecular structure. The structures of water-soluble and water-insoluble fractions from bovine lens nucleus and cortex were qualitatively compared. Reversible dependence of the lens water-soluble protein structure on water content in the system was demonstrated.

[X-ray diffraction in the intact isolated frog ocular lens]. / Difraktsiia rentgenovskikh luchei na tselom izolirovannom khrustalike glaza liagushki.

X-ray diffraction method has been applied for investigating ocular lens native tissue of the frog. X-ray diffraction patterns of intact lenses, their nuclei and cortices are similar and contain a set of concentric diffuse diffraction maxima. The most intensive of these maxima corresponding to the Bragg-spacings of 14.6, 9.1 and 4.6 A are presumably associated with intramolecular structure of lens proteins--crystallins. Intensive small-angle X-ray scattering and diffraction patterns isotropy indicates unavailability of crystallin molecule ordering or orientation in the lens. The shift of 14.6 A maximum up to 12.8 A being the result of nuclei drying shows the necessity of aqueous surrounding for these protein native structure maintenance.

[Comparative x-ray diffraction study of the crystalline lens in a number of vertebrates including man]. / Sravnitel'noe rentgenovskoe difraktsionnoe issledovanie khrustalikov glaza v riadu pozvonochnykh vkliuchaia cheloveka.

X-ray diffraction method has been applied for comparative investigation of native structure of eye lens proteins (crystallins). X-ray diffraction patterns of the whole lenses and/or their nuclear parts were obtained for man and vertebrate animals. Crystalline lenses of the fishes Acerina cernua and Pelmatochromis kribensis, frog Rana temporaria, bull and man contain crystallins with a very similar secondary and tertiary structure, whereas lenses of chicks and the tortoise Testudo horsfieldi contain mainly crystallins with other structure. The results obtained reveal evolutionary conservatism of crystallin structure in fishes, amphibians and mammals. It was also concluded that there is no correlation between crystallin structure of the lens, elasticity of the latter and accommodation mechanism.