PubMed Health⌕ Search

Biomedical subjects

T G Spiro

Publications and source records attributed to T G Spiro.

119 records · Page 7Linked to original sources
PubMed1974

Resonance Raman spectra of cobalt-substituted hemoglobin: cooperativity and displacement of the cobalt atom upon oxygenation.

The resonance Raman spectra of oxy and deoxy cobalt-substituted hemoglobin (CoHb) are reported. Comparison of these spectra to those of hemoglobin, methemoglobin, cytochrome c, and model cobalt porphyrin complexes suggests that the displacement of the cobalt atom upon oxygenation of CoHb is no greater than the out-of-plane distance in five-coordinate Co(II) porphyrins, 0.15 A. Combining this distance with the expected contraction of the cobalt-histidine bond, Ibers has estimated a maximum displacement of 0.37 A for the proximal histidine with respect to the heme plane upon oxygenation, about one-third the corresponding distance estimated for iron hemoglobin. The free energy of cooperativity for cobalt hemoglobin is also estimated to be one-third that of iron hemoglobin. These results are therefore consistent with Hopfield's distributed energy model, which predicts proportionality between proximal histidine displacement and the free energy of cooperativity. By implication they support Perutz's trigger mechanism for cooperativity.

Binding Sites↗
PubMed1972

Resonance Raman spectra of hemoglobin and cytochrome c: inverse polarization and vibronic scattering.

Resonance Raman spectra of hemoglobin and cytochrome c in dilute solution contain prominent bands that exhibit inverse polarization, i.e., the polarization vector of the incident radiation is rotated through 90 degrees for 90 degrees scattering, giving infinite depolarization ratios. This phenomenon is shown to require an antisymmetric molecular-scattering tensor. The antisymmetry, which is characteristic of resonance scattering, is associated with the form of a particular class of vibrations, A(20), of the tetragonal heme chromophores. The dependence of the resonance Raman spectra on the wavelength of the exciting radiation, as well as their polarization properties, demonstrates that the prominent bands correspond to vibronically active modes of the first electronic transition of the heme proteins, and provide confirmation of Albrecht's vibronic theory of Raman intensities.

Animals↗