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Biomedical subjects

B M Hoffman

Publications and source records attributed to B M Hoffman.

At least 109 records · Page 6Linked to original sources
PubMed1976

Anomalous azide binding to metmanganomyoglobin.

The reaction of metmanganomyoglobin (MnIIIMb) with azide presents a novel pattern with direct evidence for kinetic complexity. Although the kinetic analysis may not be unique, it appears that the azide complex cannot be fully formed, as judged by spectrophotometric changes, even with an infinitely great [N3-]. This is interpreted as resulting from an equilibrium between the final spectroscopically observable azide complex and an intermediate species whose spectrum is not substantially different from that of MnIIIMb itself. The two forms of the azide complex appear to exhibit roughly equal proportions at 3 degrees C. We propose that this intermediate is a weak Mn3+ -azide complex in which the metal ion remains out-of-plane toward the imidazole of the proximal histidine, but that the metal lies toward the anion in the "final" complex.

Animals↗
PubMed1976

Electron-nuclear double resonance in melanins.

Electron-nuclear double resonance (ENDOR) signals from matrix protons interacting with the stable free radicals of "A"- and "B"-type melanins have been observed as a function of pH. In all samples the single line is similar in width and unusually narrow. The ENDOR reduction varies by more than a factor of 10, indicating a large sensitivity of relaxation properties of melanin to sample type. Signals were observed over a wide range of experimental conditions with good signal-to-noise ratio, establishing feasibility for further more detailed ENDOR studies. Incubation in D2O resulted in little change, indicating that the free radical is well buried or protected. No resolved hyperfine structure was seen, consistent with the generally accepted view that melanin is a heterogeneous polymer.

Electron Spin Resonance Spectroscopy↗
PubMed1976

Linearity of the hemoglobin oxidation bohr effect.

The hemoglobin oxidation Bohr effect below pH 7 is essentially proportional to the fraction of hemes oxidized, just as the ligation Bohr effect is proportional to fractional heme ligation. The reported nonlinear proton release during oxidation [(1965) J. Biol. Chem. 240, 3317-3324] is shown to be an artifact resulting from the use of ferricyanide as oxidant. Published forms of the two-state allosteric transition model for hemoglobin function have used several proton linkage schemes, and none are compatible with a linear proton release upon oxidation.

Heme↗
PubMed1975

Redox equilibria of liganded forms of methemoglobin.

We have examined the redox equilibria of azidomethemoglobin (low-spin) and fluoromethemoglobin (high-spin). We have derived a modified Hill equation which includes the tetramer--dimer equilibrium of the oxidized form, and also generalized the two-state model to incorporate ligand binding to the ferriheme. The pH dependence of the redox Hill's constant for fluoromethemoglobin is the same as that for methemoglobin, demonstrating that this dependence and the marked cooperativity achieved (n = 2.2) are not coupled to changes of the ferriheme spin state. The redox Hill's constant for azidomethemoglobin, however, is as large as the oxygenation Hill's constant (n approximately 2.7) and is also roughly pH independent.

Binding Sites↗
PubMed1972

Coboglobins: heterotropic linkage and the existence of a quaternary structure change upon oxygenation of cobaltohemoglobin.

Cobaltohemoglobin prepared from horse hemoglobin retains the full heterotropic linkage properties of the normal iron hemoglobin, including both the Bohr and phosphate effects. From this result, and the known connection between heterotropic linkage properties and hemoglobin conformational change, it is concluded that cobaltohemoglobin undergoes a quaternary structure transition upon oxygenation. Thus, the stereochemical changes that occur upon oxygen binding to cobalt, as well as to iron, must be compatible with the mechanism triggering such a transition.

Animals↗
PubMed1972

Study of an oxygenated heme complex in frozen solution by Mössbauer emission spectroscopy.

We have used Mössbauer emission spectroscopy to study an oxygenated heme complex, produced in a frozen solution by nuclear decay from the isomorphous (57)Co-labeled compound. The Mössbauer parameters agree with those obtained by Mössbauer absorption spectroscopy of oxyhemoglobin. Thus, a nonprotein environment for iron can duplicate the unique oxyhemoglobin Mössbauer spectrum. The electronic structure of the heme iron in oxyhemoglobin is not significantly influenced by the protein environment. Mössbauer emission spectroscopy can be useful in the investigation of heme proteins.

Cobalt Isotopes↗