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The self-organization of helical regions of myoglobin into a compact tertiary structure is considered on the basis of the hypothesis on the step-wise mechanism of self-organization of protein molecules. It is assumed that the self-organization begins with the formation of "centers of crystallization" and proceeds with the growth of on such center or by a sequential collapse of two or more grown centers. Different pathways of self-organization of myoglobin are considered; the most favourable structures corresponding to the greatest number of dehydrated bulky hydrophobic groups and to all the strongly hydrophilic groups exposed to water are selected at every stage of the given pathway and the others are neglected. One of the two most favourable structures obtained in such a way coincides in rough resolution with the native tertiary structure of protein.
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PMID:A model of myoglobin self-organization. 112 92

220 MHz roton NMR spectral evidence for restricted rotation of one methyl group in the heme side chain of ferric horse cyanomyoglobin is reported here. Temperature dependence of this methyl proton signal was computer-simulated, yielding 14,8 kcal/mol for the methyl hindered rotation. Ionic additives such as NaCl and (NH4) 2 minus SO4 caused a slackening of this restriction of methyl rotation, evidenced from collapse of methyl signal doubling by the addition of these ionic substances. This is discussed in terms of breaking of the salt bridge formed between one of the propionate COO minus group of heme and a part of the apoprotein which might lead to constraint of one of the heme side methyl groups. The peculiarity of hyperfine-shifted methyl proton signals for other myoglobin complexes such as azide and imidazole derivatives is also discussed briefly in terms of constraint of heme side methyl group buried in a hydrophobic cleft.
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PMID:Nuclear magnetic resonance studies of hemoproteins. IV. Hindered rotation of heme side methyl group as a probe for studying van der Waals contacts in the heme side environments of myoglobin derivatives. 116 71

Studies of a stable molten globule intermediate (I) of apomyoglobin have shown that: (1) the A, G and H helices, but not the B and E helices, of myoglobin are stabilized in I, (2) individual peptides containing the G and H sequences do not show stable helix formation, although the H peptide shows partial (30%) helix formation, and (3) the mechanism by which the A, G and H helices are stabilized in I is not side chain interdigitation between helices at the helix contact sites of myoglobin. Consequently, the molten globule intermediate confers stability on the A, G and H helices, and the mechanism of stabilization is not the direct interaction found in native myoglobin. Kinetic studies of the folding reactions of small proteins have shown folding intermediates that could be either framework intermediates or molten globule intermediates, but a clear distinction between these two classes of kinetic intermediates has been lacking. An operational distinction is proposed here: molten globule intermediates are not stabilized by side chain interdigitation at contact sites between units of secondary structure found in the corresponding native protein, whereas framework intermediates are stabilized in this way. Site-directed mutagenesis experiments can distinguish between the two classes of intermediate. On the basis of this definition, the kinetic folding intermediates that are detected by far-UV circular dichroism can be molten globule intermediates, and when both a molten globule and a framework intermediate occur on the same folding pathway, the molten globule intermediate should precede the framework intermediate. Protection of individual amide protons against exchange has given the most detailed information thus far about the structures of folding intermediates in non-covalent folding reactions. It is possible that amide proton protection might occur during folding either by a non-specific mechanism, such as a hydrophobic collapse, or by the formation and later breakdown of non-native secondary structure; either event would pose a serious problem for interpretation of the results. Tests are available for assessing whether either event occurs, and they are discussed here.
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PMID:Experimental studies of pathways of protein folding. 166 33

In comparison with myoglobin and human and Glycera dibranchiata hemoglobins, the heme distal side amino acid exchanges within the heme environment of elephant tetrameric hemoglobin (Hbe) only slightly affect the electronic and ESR spectra of Hbe(III) and Hbe(II) derivatives, several of which were prepared and characterized by optical and ESR spectroscopy. Addition of 2,3-bisphosphoglycerate [Gri(2,3)P2] or inositol hexakisphosphate to Hbe(II)NO causes tension in the Fe-N(proximal His) bond, although the behaviour differs in detail from that of HbA(II)NO. There are two equilibrium states of Hbe having significantly different kinetics for the Hbe(III)----Hbe(II) reaction of Hbe(III)NO. This autoreduction occurs in the form of two parallel processes, which collapse into one intermediate rate in the presence of Gri(2,3)P2. The temperature dependences of the rates enable deduction of delta H0 and delta S0 for the linked equilibrium, and yield linear Eyring plots for Hbe(III)NO, from which activation parameters were estimated on the basis of a previously described mechanism.
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PMID:Spectroscopic and kinetic aspects of Elephas maximus hemoglobin. 215 90

The effects of high pressure (0.1-3.4 gigapascal (GPa)) on the ferrous heme active sites of human adult hemoglobin, sperm whale myoglobin, and Glycera dibranchiata hemoglobin (Fraction II) were probed using resonance Raman and absorption spectroscopies. High-to-low spin transitions of the heme iron occur for hemoglobin, myoglobin, and Glycera hemoglobin at 0.35, 0.75, and 0.50 GPa, respectively, for the deoxy species. These interspecies differences result from variations in the composition of the hemepockets and/or their rigidity to pressure-induced volume changes. Heme active sites initially bound to CO or O2 exhibit distinctive behavior at high pressures. For all proteins studied, O2 apparently dissociates from the heme at only moderately high pressure, while CO remains bound to the heme moiety even at extreme pressures. The Raman spectra demonstrate the differences in the ligated and deoxy species at 3.4 GPa in the high frequency region. Discrete changes (i.e. iron spin-state transitions and dissociation of O2) occur that are commensurate with the collapse of the distal pocket, while continuous shifts in the absorption and Raman spectra are observed at pressures above those required for pocket collapse.
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PMID:The effects of high pressure upon ligated and deoxyhemoglobins and myoglobin. An optical spectroscopic study. 291 87

The 13C-NMR spectra of high-spin met-aquo myoglobin, spin-equilibrium met-azido myoglobin, low-spin met-cyano myoglobin, deoxy myoglobin and carbonmonoxy myoglobin from sperm whale reconstituted with hemin 13C enriched at both vinyl alpha or beta positions have been recorded. In all cases the labeled vinyl 13C signals are clearly resolved and useful spectra could be obtained within approx. 15 minutes. The decoupling of multiplet structure due to attached proton(s) has led to the specific assignment of vinyl 13C alpha signals in all paramagnetic derivatives and the 13C beta signals in met-cyano myoglobin. In all other cases, the collapse of the proton multiplet structure as a function of 1H decoupling frequency has located, but not assigned, the attached 1H resonance positions which are obscured by the intense diamagnetic envelope in the 1H-NMR spectrum. The resulting vinyl 13C hyperfine shifts follow Curie behavior, and the patterns closely resemble those in the appropriate model complexes in the same oxidation/spin/ligation state, except that the protein exhibits more in-plane asymmetry. The hyperfine shift patterns are indicative of dominant pi contact shifts for all ferric complexes. Deoxy myoglobin vinyl 13C and 1H contact shifts provide little evidence for pi bonding.
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PMID:13C-NMR study of labeled vinyl groups in paramagnetic myoglobin derivatives. 382 62

Although rare, exertional collapse and sudden death are the most serious potential complications of sickle cell trait. Studies suggest that this condition may occur in susceptible persons when poor physical conditioning, dehydration, heat stress or hypoxic states precipitate sickling of the abnormal erythrocytes. Sickling leads to endothelial damage, which can cause vasoconstriction, disseminated intravascular coagulation and local tissue damage. Cardiac effects include acute ischemia and arrhythmias. Muscle damage results in acute compartment syndromes and release of myoglobin into the circulation. Acute renal failure is possible. Diagnosis is based on a high index of suspicion, and characteristic presentation and laboratory findings, including myoglobinuria, hyperkalemia, hypocalcemia, hyperphosphatemia and elevated creatine kinase levels. The differential diagnosis includes pulmonary embolism, acute cardiac events, anaphylaxis and heat stroke. Management is based on stabilization, rehydration, and the treatment and prevention of complications.
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PMID:Exertional collapse and sudden death associated with sickle cell trait. 904 99

Temperature-induced denaturation transitions of different structural forms of apomyoglobin were studied monitoring intrinsic tryptophan fluorescence. It was found that the tryptophans are effectively screened from solvent both in native and acid forms throughout most of the temperature range tested. Thus, the tryptophans' surrounding do not show a considerable change in structure where major protein conformational transitions have been found in apomyoglobin using other techniques. At high temperatures and under strong destabilizing conditions, the tryptophans' fluorescence parameters show sigmoidal thermal denaturation. These results, combined with previous studies, show that the structure of this protein is heterogeneous, including native-like (tightly packed) and molten globule-like substructures that exhibit conformation (denaturation) transitions under different conditions of pH and temperature (and denaturants). The results suggest that the folding of this protein proceeds via two "nucleation" events whereby native-like contacts are formed. One of these events, which involves AGH "core" formation, appears to occur very early in the folding process, even before significant hydrophobic collapse in the rest of the protein molecule. From the current studies and other results, a rather detailed picture of the folding of myoglobin is presented, on the level of specific structures and their thermodynamical properties as well as formation kinetics.
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PMID:Structural heterogeneity of the various forms of apomyoglobin: implications for protein folding. 933 36

There is wide diversity in the animals that dive to depth and in the distribution of their body oxygen stores. A hallmark of animals diving to depth is a substantial elevation of muscle myoglobin concentration. In deep divers, more than 80% of the oxygen store is in the blood and muscles. How these oxygen stores are managed, particularly within muscle, is unclear. The aerobic endurance of four species has now been measured. These measurements provide a standard for other species in which the limits cannot be measured. Diving to depth requires several adaptations to the effects of pressure. In mammals, one adaptation is lung collapse at shallow depths, which limits absorption of nitrogen. Blood N2 levels remain below the threshold for decompression sickness. No such adaptive model is known for birds. There appear to be two diving strategies used by animals that dive to depth. Seals, for example, seldom rely on anaerobic metabolism. Birds, on the other hand, frequently rely on anaerobic metabolism to exploit prey-rich depths otherwise unavailable to them.
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PMID:The physiological basis of diving to depth: birds and mammals. 955 52

Push/pull hemodiafiltration (HDF) is characterized by alternate repetition of filtration and backfiltration during hemodialysis with high-flux membrane. In the pressure-controlled push/pull (PC P/P) HDF system, which is the newest push/pull HDF system, there are about 25 repetitions of dilution and concentration of the blood while it passes through the hemodiafilter. Hence, the PC P/P is functionally close to the predilution mode of on-line HDF. In the PC P/P, body fluid is replaced usually by more than 120 L of dialysate during the 4 h treatment. In selecting a hemodiafilter for PC P/P, one must be certain that the blood flow channels in the hemodiafilter do not collapse by the positive pressure on the dialysate side in the backfiltration phase. Thus, the polyacrylonitrile hollow-fiber hemodiafilter and polysulfon hollow-fiber hemodiafilter are suitable for PC P/P. In the short term, PC P/P has been reported to be effective against joint pain, itchiness, insomnia, irritability, and restless leg syndrome experienced by hemodialysis patients. Midterm clinical effectiveness of PC P/P includes the requisite lowering of the erythropoietin dose and improvement in skin pigmentation. The albumin loss per treatment with the PC P/P was significantly lower than that with the conventional HDF approach when a protein-permeable membrane is used. In terms of the removal rate of prolactin, no significant difference was found between PC P/P and conventional HDF. On the other hand, the removal rates of myoglobin and beta2M, where molecular size was smaller than prolactin, was significantly greater with the PC P/P than with conventional HDF.
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PMID:Push/pull hemodiafiltration: technical aspects and clinical effectiveness. 1061 32


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