title: Orientation of the hemes of high potential cytochromes relative to photosynthetic membranes, as shown by the linear dichroism of oriented preparations.
abstract: The orientations of high potential cytochromes with respect to photosynthetic membranes was investigated in spinach chloroplasts and in Rhodopseudomonas viridis. The general approach consists in detection with polarized light of photoinduced absorbance changes related to the oxidation of the cytochromes. The orientation of cytochrome c-558 was measured at room temperature in chromatophores and whole cells of Rps. viridis, oriented on glass slides and in a magnetic field, respectively. The orientation of cytochrome b-559 of green plants was detected at 77 K in magnetically oriented chloroplasts. In both cases the dichroic ratio for the alpha band shows that the heme plane makes an angle greater than 35 degrees C with the membrane plane. Moreover, the dichroic ratio is not constant throughout the alpha and beta bands, for both cytochrome c-558 and b-559. Linear dichroism spectra of oriented pure horse heart cytochrome c and cytochrome c2 of Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films show that the variations of the dichroic ratio in the alpha and beta bands can be explained by the occurrence of x- and y-polarized transitions absorbing at slightly different wavelengths.
mesh_terms: D002736:Chloroplasts / Q000502:physiology; D003580:Cytochromes / Q000378:metabolism*; D004574:Electromagnetic Fields; D006418:Heme; D007425:Intracellular Membranes / Q000502:physiology; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D010788:Photosynthesis; D012241:Rhodopseudomonas / Q000502:physiology*; D013057:Spectrum Analysis
chemical_list: D003580:Cytochromes; D006418:Heme