Several forms of chromaffin granule cytochrome b-561 revealed by EPR spectroscopy.
Low-temperature EPR spectra of chromaffin granule membranes from bovine adrenal medulla reveal 3 different signals of the ferric cytochrome b-561. A typical gZ signal of a low-spin cytochrome observed at g approximately 3 is comprised of a high-potential component with gZ = 3.14 and a low-potential one with gZ = 3.11, the low-potential signal showing significantly faster relaxation. In addition, a highly temperature-sensitive heme signal at g = 3.7 is observed which is fully retained in the preparation of granule membranes with b-561 reduced by 50% but disappears upon full reduction of the cytochrome by ascorbate. The signal is strikingly similar to that of the mitochondrial low-potential cytochrome b heme (bL or b-566). The presence of several forms of b-561 in chromaffin granule membranes may provide a structural basis for the transmembrane electron transfer believe to be catalyzed by this hemoprotein.
Burbaev
D Sh
DSh
N.N. Semenov Institute of Chemical Physics, Acad. Sci. USSR, Moscow.
Moroz
I A
IA
Kamenskiy
Y A
YA
Konstantinov AuA
D000818:Animals; D002417:Cattle; D002837:Chromaffin Granules / Q000201:enzymology*; D003573:Cytochrome b Group / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D013696:Temperature
D003573:Cytochrome b Group; C023646:cytochrome b561