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PubMed1975

NMR studies of hemoproteins. VI. Acid-base transitions of ferric myoglobin and its imidazole complex.

220 MHz proton NMR was applied to the acid-base transition of ferric myoglobin and its imidazole complex. In horse and sperm whale ferric myoglobins: (1) pH-dependent shift of heme-ring methyl signals above p2H 10 was analyzed on the basis of rapid exchange between alkaline and acidic forms by the use of pK value 9.1 of acid-base transition in 1H20 solution; (2) limiting shifts of three methyl signals were reasonably determined for purely alkaline form. For the imidazole complex: (3) a drastic high field shift of each signal was observed above p2H 9.0, whereas N0methyl imidazole complex did not exhibit such a shift, which suggests the 2H+ dissociation from liganded imidazole greater than N2H. It is concluded thns.

Animals↗
PubMed1978

Proton NMR study of the thermodynamics and kinetics of the acid in equilibrium base transitions in reconstituted metmyoglobins.

Optical and proton NMR pH titrations of sperm whale metmyoglobin (metMb) in its native form and reconstituted with chemically modified hemes reveal that the pKa for the acid in equilibrium base transition decreases as the heme 2,4-substituents are made more electron withdrawing. The proton NMR spectra yields resonances which are averaged over the acidic and basic forms of the protein, but still exhibit significant exchange line broadening. Analysis of this exchange contribution to the linewidth is consistent with the simple kinetic scheme metMb+H2O + OH- k2 in equilibrium k1 metMbOH + H2O with k2 = 1.3 +/- 0.5 . 10(10) M-1 . s-1 and k1 = 1.6 +/- 0.6 . 10(5) s-1 for the native protein. The effect of electron-withdrawing substituents on the heme increase k2 and decrease k1.

Animals↗
PubMed1979

Transient intermediates in the reduction of Fe(III) myoglobin-ligand complexes by electrons at low temperature.

1. The reductions of a number of sperm-whale Fe(III) myoglobin-ligand complexes by electrons generated by gamma-irradiation in ethylene glycol/water glass, have been investigated by using low-temperature spectrophotometry. The ligands are azide, fluoride, imidazole and water. 2. The reduction of the Fe(III) myoglobin-ligand complexes at 77 K leads to the formation of low-spin liganded Fe(II) myoglobin, in the case of the azide, imidazole and water derivatives, while the reduction of the fluoride derivative proceeds both by a pathway involving prior dissociation of the ligand and with the ligand in position. 3. Investigation of the effect of temperature on the stability of the Fe(II) myoglobin-ligand complexes indicates that more than one bound states exists in dissociation of the ligand molecule from the ferrous heme iron of the reduced azide and imidazole derivatives. 4. The results are discussed in terms of the possible structure of the Fe(II) myoglobin complexes and it is suggested that the low-spin state is created by a strained configuration of the heme center with the iron atom in an intermediate position relative to the heme plane.

Animals↗
PubMed1979

Influence of steric factors on oxygen binding. I. Studies on 2,4-diisopropyldeuteroheme-myoglobin.

Sperm whale apomyoglobin was recombined with 2,4-diisopropyldeuterohemin to form 2,4-diisopropyldeuteroheme-myoglobin and its various physico-chemical properties were investigated to get an insight into the structural and functional role of the peripheral vinyl groups. 2,4-Diisopropyldeuteroheme-myoglobin showed a four times lower oxygen affinity at 25 degrees C and larger enthalpy and entropy changes of oxygenation than the corresponding values of native myoglobin. 2,4-Diisopropyldeuteroheme-metmyoglobin shows a pKa value of 9.68 which is higher than those of native metmyoglobin and mesoheme-metmyoglobin. The rate of autooxidation of oxy-form was about seven times larger in 2,4-diisopropyldeuteroheme-myoglobin than in native myoglobin. The electron-donating effect of isopropyl groups does not give straightforward explanation for these anomalous properties of 2,4-diisopropyldeuteroheme-myoglobin. It is proposed that site and stereospecific van der Waals' interaction between the polypeptide side chains and the peripheral 2,4-diisopropyl groups may weaken the interaction between the bound oxygen molecule and the distal His, resulting in the decrease in the stability of oxyform.

Animals↗
PubMed1980

Heme methyl hyperfine-shifted nuclear magnetic resonance peaks assigned by selective deuteration as indicators of heme-protein interactions in metmyoglobins.

The heme methyl resonances in a variety of high-spin, low-spin and spin-equilibrium forms of sperm whale metmyoglobin have been assigned by reconstituting myoglobin with selectively deuterated hemes. Two patterns for the heme methyl hyperfine shifts are observed, one characteristic of the low-spin state and the other typical of the high-spin state. The two protein forms which can change the position of their spin equilibrium significantly with changing temperature exhibit the pattern of the dominant spin state component at any temperature. The different hyperfine shift patterns for the low-spin and high-spin states are concluded to arise not from different heme-protein contacts in the two spin states, but from characteristic differential sensitivities of the dominant spin transfer mechanisms to the same rhombic perturbation.

Animals↗
PubMed1985

Iron-57 chemical shifts in carbonyl myoglobin and its model complexes determined by iron-57-carbon-13 double resonance.

The 57Fe chemical shift of sperm whale carbonyl myoglobin and two model complexes have been determined by double resonance methods in doubly enriched [57Fe, 13C] samples. Deprotonation of the axial imidazole in the model complex causes a large upfield 57Fe chemical shift, consistent with the increased ligand field strength. The 57Fe signal for MbCO is to low field of that of the neutral imidazole complex, arguing against significant hydrogen-bonding of its imidazole but supporting a slight axial strain. This indirect method permits the first effective study of 57Fe shifts in a limited class of hemoproteins.

Animals↗
PubMed1986

Picosecond geminate recombination of nitrosylmyoglobins.

The kinetics of NO geminate recombination to sperm whale and elephant myoglobins has been studied on the picosecond time scale using an amplified colliding-pulse mode-locked ring dye laser. The dynamics of ligand rebinding are shown to be affected by the distal structure of the protein surrounding the heme pocket.

Animals↗
PubMed1987

Microbore HPLC/mass spectrometry for the analysis of peptide mixtures using a continuous flow interface.

Microbore HPLC techniques have been combined with fast atom bombardment mass spectrometry to provide HPLC/MS capabilities for the analysis of mixtures of peptides and small proteins. The interface between the liquid chromatograph and mass spectrometer is a continuous flow direct insertion probe which contains a fused silica capillary that delivers the eluting solvent to the FAB source of the mass spectrometer at a rate of 5-10 microL/min. Data are presented for the analysis of several mixtures of peptides ranging in molecular weights from about 900 to 6000 daltons. In addition, the analysis of 100 pmol of a tryptic digest of whale myoglobin is shown where 16 of the possible 19 peptides were identified in the mass range m/z 2200-250. The advantages of this approach to HPLC/MS are a relatively high sensitivity because of the low flow rates and low background, and the ability to detect high molecular weight compounds.

Animals↗
PubMed1983

Hydrophobic-interaction chromatography of glycosaminoglycuronans: the contribution of N-acetyl groups in heparin and heparan sulfate to the affinity for hydrophobic gels, and variety of molecular species in beef-kidney heparan sulfate.

Contribution of N-acetyl groups in heparin and heparan sulfate to their affinity for hydrophobic gels was examined by use of a series of semi-synthetic, N-acetylated, hog-intestinal heparins, a whale-intestinal heparin, and a beef-kidney heparan sulfate. Chromatography on Phenyl-Sepharose CL-4B in 3.8-1.0M ammonium sulfate-10mM hydrochloric acid indicated that an increasing N-acetyl content, which is correlated to a decreasing N-sulfate content, results in a marked increase in the affinity for the gels. The variety of molecular species in beef-kidney heparan sulfate, previously fractionated by conventional chromatographic procedures, was demonstrated by separating further, by hydrophobic-interaction chromatography, the polysaccharide into several fractions composed of molecular species distinctly different in N-acetyl and sulfate content, and in molecular size.

Animals↗
PubMed1989

Conformation of a T cell stimulating peptide in aqueous solution.

Using two-dimensional NMR spectroscopy and circular dichroism spectroscopy it is demonstrated that a T cell stimulating peptide corresponding to residues 132-153 of sperm whale myoglobin populates helical conformations in aqueous solution. This finding is in accordance with proposals that immunodominant sites in T cell stimulating peptides have a high conformational propensity. The observation of secondary structure in aqueous solutions of this and other immunogenic peptides has important implications for initiation of protein folding.

Amino Acid Sequence↗
PubMed1991

Relative-residue surface-accessibility patterns reveal myoglobin and catalase similarity.

A novel sliding-window search method using relative-residue surface-accessibility patterns identified extensive, but unsuspected, structural similarity over a 3-helix region in the C-terminus of the evolutionarily unrelated proteins sperm-whale myoglobin and beef liver catalase. This clear example of structural similarity between non-homologous proteins highlights the importance of relative-residue surface-accessibility patterns in understanding the local folded structure in proteins.

Amino Acid Sequence↗
PubMed1992

Anomalous reversed-phase high-performance liquid chromatographic behavior of synthetic peptides related to antigenic helper T cell sites.

Sets of overlapping synthetic peptides for three well characterized proteins (sperm whale myoglobin, hen egg lysozyme, and the circumsporozoite protein from Plasmodium falciparum) were prepared and examined by reversed-phase high-performance liquid chromatography (RP-HPLC). Using retention coefficients to predict the retention time of each peptide, several peptides in each protein set were found that exhibited anomalous behavior (i.e. eluted significantly later than predicted). Previous work with model peptides has shown that this anomalous behavior can be attributed to specific amphipathic arrangements induced by the lipid stationary phase during the RP-HPLC process. In the current study it was found that although not all of the peptides containing an antigenic T cell site displayed anomalously late behavior, all of the peptides which eluted anomalously late during RP-HPLC included the regions of these proteins known from earlier studies to be antigenic T cell sites.

Amino Acid Sequence↗
PubMed1984

Aplysia oxymyoglobin with an unusual stability property.

Native oxymyoglobin was isolated directly from the radular muscle of Aplysia kurodai with complete separation from metmyoglobin on a DEAE-cellulose column. It was examined for its spectral and stability properties. The spectrum of Aplysia MbO2 , which lacks the distal histidine, is very similar to those of mammalian oxymyoglobins , the alpha-peak being higher than the beta-peak and the absorbance ratio being 1.03. Its stability, however, is quite different from those of the mammalian oxymyoglobins , and Aplysia MbO2 is found to be extremely susceptible to autoxidation. Its rate is one-hundred times higher at pH 9.0, and its pH dependence is unusual and much less steep, when compared with sperm whale MbO2 as reference.

Animals↗
PubMed1984

Aplysia myoglobins with an unusual amino acid sequence.

The complete amino acid sequence of the myoglobin from Aplysia juliana, a species distributed world-wide, has been determined and compared with the sequence of the myoglobin of Aplysia limacina, a Mediterranean species, and of Aplysia kurodai, a Japanese and Asian species. Unlike mammalian myoglobins, Aplysia myoglobins contain only a single histidine residue, lacking the distal one, the homology being 76% between A. juliana and A. limacina, 74% between A. juliana and A. kurodai, and 83% between A. limacina and A. kurodai. The hydropathy profiles of the Aplysia myoglobins are very similar, but completely different from that of sperm whale myoglobin, taken as the reference.

Amino Acid Sequence↗
PubMed1986

Cold denaturation of myoglobin.

The stability of the structure of sperm whale metmyoglobin has been studied in various solutions, in the temperature range -8 degrees C to 100 degrees C, by scanning microcalorimetry, light absorption, circular dichroism, nuclear magnetic resonance spectroscopy and viscosimetry. It has been shown that in 10 mM-sodium acetate solutions (pH 3.5 to 3.9) the protein molecule undergoes a reversible conformational transition into a non-compact disordered state not only when the solution is heated above room temperature but also when it is cooled. In this state the protein does not have a tertiary structure, although it retains some residual ellipticity, which may be caused by the fluctuating alpha-helical conformation of the unfolded polypeptide chain. The disruption of the native protein structure both on cooling (cold-denaturation) and on heating (heat-denaturation) proceeds in an "all-or-none" manner, with a significant and similar increase of the protein heat capacity, but with inverse enthalpic and entropic effects: the enthalpy and entropy of the protein molecule decrease during cold-denaturation and increase during heat-denaturation.

Animals↗
PubMed1988

Thermodynamic study of the apomyoglobin structure.

Sperm whale apomyoglobin has been studied thermodynamically in solutions with different pH and temperature by scanning microcalorimetry, viscosimetry, nuclear magnetic resonance and circular dichroism spectrometry, and by electrometric and calorimetric titration. It has been shown that apomyoglobin in solutions with pH close to neutral has a compact and unique spatial structure with an extended hydrophobic core. This structure is maximally stable at about 30 degrees C and breaks down reversibly both upon heating or cooling from this temperature. The process of breakdown of this structure is highly co-operative and can be regarded as a transition between two macroscopic states of protein, the native and denatured states. In contrast to the native state, which is specified by definite values of compactness and ellipticity, the compactness and ellipticity of the denatured state of apomyoglobin depend strongly on pH; with a decrease of pH below 4.0, these parameters gradually approach the values of the random coil.

Animals↗
PubMed1991

A simplified mechanical model of proteins tested on the globin fold.

It has been shown that the distribution of presently known protein loop lengths is consistent with even the simplest available theory of rubber-like elasticity, and with the idea that such loops generate an entropically derived end-to-end tension. It has also been asserted that the molten globule phase, just like the native form, must be mechanically stable, and that a simple demonstration of the potential for mechanical stability would be a powerful test in predictions of new protein folds. This paper amplifies this suggestion by explicit calculation of a familiar but non-trivial test case: sperm-whale myoglobin. The method used is to describe the protein molecule in terms of a highly simplified mechanical model bearing some resemblance to a pre-stressed mechanism. The alpha-helices are treated as rigid rods and the loops are treated as elastic strings. The entropic tensions exerted by the loops are imposed on the mechanism using an approximation proposed earlier. The helices are then held to generate frictionless reaction forces at their mutual points of contact. These contact forces are calculated to null out maximally the effects of the loop tensions, and hence stabilize the molecule. It is shown that the crystallographically determined structure of myoglobin has a significantly higher mechanical stability on this model than does any of a previously published set of combinatorially generated predictions. Amongst the predictions alone, the best is also the one with the highest stability. It is anticipated that this result could be of general importance in sorting or filtering out bad predictions. A further exciting feature of the model is that it offers a natural explanation for the strong conservation of the C2 proline and the invariably long unconserved sequence from the end of the C helix to the start of the E helix in the globins and phycocyanins.

Animals↗