Variable-Temperature ESI-IMS-MS Analysis of Myohemerythrin Reveals Ligand Losses, Unfolding, and a Non-Native Disulfide Bond.

Variable-temperature electrospray ionization combined with ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques are used to monitor structural transitions of the protein myohemerythrin from peanut worm in aqueous ammonium acetate solutions from ∼15 to 92 °C. At physiological temperatures, myohemerythrin favors a four-helix bundle motif and has a diiron oxo cofactor that binds oxygen. As the solution temperature is increased from ∼15 to 35 °C, some bound oxygen dissociates; at ∼66 °C, the cofactor dissociates to produce populations of both folded and unfolded apoprotein. At higher temperatures (∼85 °C and above), the IMS-MS spectrum indicates that the folded apoprotein dominates, and provides evidence for stabilization of the structure by formation of a non-native disulfide bond. In total, we find evidence for 18 unique forms of myohemerythrin as well as information about the structures and stabilities of these states. The high-fidelity of IMS-MS techniques provides a means of examining the stabilities of individual components of complex mixtures that are inaccessible by traditional calorimetric and spectroscopic methods.

Decreased conduit perfusion measured by spectroscopy is associated with anastomotic complications.

BACKGROUND: Gastric conduit ischemia during esophagectomy likely contributes to high anastomotic complication rates, yet we lack a reliable method to assess gastric conduit perfusion. We hypothesize that optical fiber spectroscopy (OFS) can reliably assess conduit perfusion and that the degree of intraoperative gastric ischemia is associated with subsequent anastomotic complications. METHODS: During esophagectomy, OFS was used to measure oxygen saturation (SaO(2)) and blood volume fraction (BVF) in the distal gastric conduit at baseline and after gastric devascularization, conduit formation, and transposition. The SaO(2) and BVF readings were correlated to clinical outcomes. RESULTS: The OFS measurements were obtained in 23 patients during esophagectomy, four of whom previously underwent gastric ischemic conditioning. Eight patients developed anastomotic complications. Compared with baseline, conduit creation produced a 29.4% reduction in SaO(2) (p < 0.01), while BVF increased by 28% (p = 0.06). Patients with subsequent anastomotic complications demonstrated a 52.5% decrease in SaO(2) upon conduit creation compared with 15.1% in patients without complications (p = 0.01). Patients who underwent ischemic conditioning did not develop significant changes in SaO(2) (p = 0.72) or BVF (p = 0.5) upon gastric conduit creation. CONCLUSIONS: Intraoperative OFS demonstrates significant alterations in gastric conduit oxygenation during esophageal replacement, which may be tempered by gastric ischemic conditioning. The degree of intraoperative gastric ischemia resulting from gastric conduit creation is associated with the development of anastomotic complications, suggesting that OFS is useful for assessing changes in conduit oxygenation during esophagectomy. Further studies are needed to refine this technology and investigate the clinical utility of intraoperative conduit oxygenation data.

Relationship between the prefrontal function during a cognitive task and the severity of the symptoms in patients with panic disorder: a multi-channel NIRS study.

To investigate whether prefrontal function during a cognitive task reflects the severity of panic disorder, the prefrontal function during a word fluency task in 109 panic disorder patients with or without agoraphobia was measured by multi-channel near-infrared spectroscopy (NIRS). [Oxy-Hb] changes in the left inferior prefrontal cortex were significantly associated with the frequency of panic attacks, and, in addition, [deoxy-Hb] changes in the anterior area of the right prefrontal cortex were significantly associated with the severity of agoraphobia. These results suggest that the prefrontal function in patients with panic disorder is associated with the disease state of disease in patients with panic disorder.

[Freeze-drying of oxygen-carrying substances and storage stability of the freeze-dried solids].

Oxygen-carrying substances based on poly-placental hemoglobin were put into freeze-drying. Sucrose was chosen to inhibit the methmoglobin(MetHb) formation. MetHb content, ultravioletes(UV) spectrum, Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), High performance liquid chromatography (HPLC) were monitored during freeze-drying. As a result, when the mass ratio of sucrose to protein was above 0.5, MetHb formation was under control;the characteristic absorption of UV spectrum, SDS-PAGE and HPLC showed no visible change. Freeze-dried solids were kept under room temperature and refrigerator for 3 months. As a result, MetHb formation depended upon storage temperature and the mass ratio of sucrose to protein. For group C in which the mass ratio of sucrose to protein was 1.0; there is no marked change in MetHb content, UV spectrum, SDS-PAGE and HPLC after 3 months.

Visible reflectance hyperspectral imaging: characterization of a noninvasive, in vivo system for determining tissue perfusion.

We characterize a visible reflectance hyperspectral imaging system for noninvasive, in vivo, quantitative analysis of human tissue in a clinical environment. The subject area is illuminated with a quartz-tungsten-halogen light source, and the reflected light is spectrally discriminated by a liquid crystal tunable filter (LCTF) and imaged onto a silicon charge-coupled device detector. The LCTF is continuously tunable within its useful visible spectral range (525-725 nm) with an average spectral full width at half-height bandwidth of 0.38 nm and an average transmittance of 10.0%. A standard resolution target placed 5.5 ft from the system results in a field of view with a 17-cm diameter and an optimal spatial resolution of 0.45 mm. The measured reflectance spectra are quantified in terms of apparent absorbance and formatted as a hyperspectral image cube. As a clinical example, we examine a model of vascular dysfunction involving both ischemia and reactive hyperemia during tissue reperfusion. In this model, spectral images, based upon oxyhemoglobin and deoxyhemoblobin signals in the 525-645-nm region, are deconvoluted using a multivariate least-squares regression analysis to visualize the spatial distribution of the percentages of oxyhemoglobin and deoxyhemoglobin in specific skin tissue areas.

Nigerythrin and rubrerythrin from Desulfovibrio vulgaris each contain two mononuclear iron centers and two dinuclear iron clusters.

The trivial name 'rubr-erythrin' is a contraction of two other trivial names: rubredoxin (ruber, red) and hemerythrin. It names a protein of undetermined biological function which putatively carries rubredoxin-like mononuclear iron and hemerythrin-like dinuclear iron. The name 'nigerythrin' (niger, black) is an analogy of rubrerythrin. It identifies a second protein of undetermined function which has prosthetic groups similar to rubrerythrin. Rubrerythrin was initially described [LeGall, J., Prickril, B. C., Moura, I., Xavier, A. V., Moura, J. J. G. & Huynh, B.-H. (1988) Biochemistry 27, 1636-1642] as a homodimer with four iron ions arranged into two rubredoxin sites and one inter-subunit dinuclear cluster. Nigerythrin is a novel protein. Here, we report that both proteins are homodimers, each dimer carrying not four but six iron ions in two mononuclear centers and two dinuclear clusters. Rubrerythrin and nigerythrin are probably both located in the cytoplasm; they are differentially characterized with respect to molecular mass, pI, N-terminal sequence, antibody cross-reactivity, optical absorption, EPR spectroscopy, and reduction potentials. All three reduction potentials in both proteins are > +200 mV. These appear too high to be of practical relevance in the cytoplasm of the sulfate reducer Desulfovibrio vulgaris (Hildenborough). We suggest the possibility of a non-redox role for both proteins with all six iron ions in the ferrous state.

Myohemerythrin from the sipunculid, Phascolopsis gouldii: purification, properties and amino acid sequence.

Two previously unknown isoforms, labelled iso I and iso II, of the oxygen-carrying protein, myohemerythrin, have been isolated from carcasses of the sipunculid worm, Phascolopsis gouldii. The two isoforms have non-identical N-terminal amino acid sequences and slightly different absorption spectra in the met form. Far-ultraviolet circular dichroism shows that iso I contains approximately 69% alpha-helix. The complete amino acid sequence for iso I was obtained. The molecular weight calculated from this amino acid sequence and including the active site Fe-O-Fe unit, is 13,829. All of the physical and chemical properties of iso I noted above, including the amino acid sequence, are very similar to those of T. zostericola myohemerythrin. Except for the amino acid sequence, these properties are also very similar to that of a subunit in hemerythrin, the octameric analog found in hemerythrocytes. Only 58 of the 113 residues in P. gouldii hemerythrin are conserved in iso I. Sequence comparisons were used to help identify residues responsible for maintaining the common tertiary and diiron site structures in hemerythrin and myohemerythrin. The seven iron ligand residues previously identified in crystal structures of hemerythrin and myohemerythrin are conserved in iso I. However, none of the ten residue pairs previously identified as engaging in direct salt-bridge or hydrogen bond interactions between subunits in the hemerythrin octamer are conserved in iso I.

The amino acid sequence of hemerythrin from Siphonosoma cumanense.

The amino acid sequence of hemerythrin from Siphonosoma cumanense was determined. The sequence consists of 113 amino acid residues. High homology is conserved in the regions of amino acid residues coordinating two iron atoms as its active site. The invariant sequences observed from the proteins in the same family were considerably altered except for the residues in the active site.

Hemerythrin from Lingula unguis consists of two different subunits, alpha and beta.

Hemerythrin, a non-heme Fe-protein, of Lingula unguis has an octamer structure. We demonstrated that the protein is composed of two distinct subunits (alpha and beta), in equal amounts by investigation of their composition and partial terminal sequence. The cross-linking reaction of the native protein with dithiobis-(succinimidyl propionate) provided evidence for the presence of a dimer composed of alpha and beta subunits.

Crystallization and preliminary X-ray diffraction study of a protein with a high potential rubredoxin center and a hemerythrin-type Fe center.

A newly discovered iron-containing protein, isolated from the bacterium Desulfovibrio vulgaris (Hildenborough, NCIB 8303), has been crystallized. The molecule appears to be a dimer of mass 44kDa. This protein has iron centers with spectrascopic similarities to those in rubredoxins and in hemerythrins. The X-ray diffraction shows symmetry consistent with space group I222 or I212121. Cell parameters are a = 49.2 A, b = 81.3 A, c = 100.1 A, and alpha, beta, gamma = 90 degrees. X-ray diffraction data have been collected to 3.0 A, and a search for useful heavy atom derivatives is in progress for the analysis of the crystal structure of this Fe-protein.

Computer prediction of potential immunogenic determinants from protein amino acid sequence.

In proteins, immunogenic determinants that can induce protein-reactive antipeptide antibodies reside mostly in those parts of the molecule that have a high tendency to form beta-turns. A program for an IBM personal computer which predicts protein immunogenic determinants is described. The program predicts potential immunogenic determinants from protein amino acid sequences according to a Chou-Fasman-based probability of a beta-turn occurrence, p greater than 1.5 X 10(-4)(P. Y. Chou and G. D. Fasman, 1978, Adv. Enzymol. 47, 46-148). Oncopeptides (whose efficacy in generating protein-reactive antipeptide antibodies has been described) with a beta-turn probability of p greater than 1.5 X 10(-4) elicited antipeptide antibodies that reacted with the parent oncoprotein at a rate of 96%, thus showing a surprisingly good correlation between the tendency to form a beta-turn and the protein reactivity of antipeptide antibodies. Potential immunogenic determinants were predicted on myohemerythrin and myoglobin.

Active site structures of deoxyhemerythrin and oxyhemerythrin.

The physiologically active forms of the nonheme-iron, oxygen-transport protein hemerythrin have been studied by x-ray crystallographic techniques. At 3.9-A resolution, a difference electron-density map between the deoxy form and met form (methemerythrin) of the protein suggests only small differences in the binuclear iron complexes. The coordination of the iron atoms appears to be the same in both the deoxy and met forms, one iron of the complexes being pentacoordinate, the other iron being hexacoordinate. The iron atoms appear to be somewhat farther apart in the deoxy form. A 2.2-A resolution study of oxyhemerythrin shows that dioxygen binds to one iron atom--the pentacoordinate one in the met form of the protein, the same binding site found for azide in azidomethemerythrin.

Stoichiometric characteristics and resonance Raman spectra of azidosemimethemerythrin.

With extra precautions to remove dissolved oxygen, reduction of aquomethemerythrin with dithionite occurs with a stoichiometry very close to 1.0. The aquosemimethemerythrin so produced combines with N3- ion almost on a 1:1 basis per monomer. Resonance Raman spectra of azidosemimethemerythrin differ from those of azidomethemerythrin in the position of the Fe-N stretching frequency and in the absence of a feature corresponding to a mu-oxo bridge, but in both complexes the internal azide stretch occurs at the same frequency and the substitution of isotopically unsymmetrical 15N14N-2 leads to a splitting of the Fe-N band. These observations provide some insight into the structural features of the binuclear functional site.