A model for the molecular organization of cytochrome beta-561 in chromaffin granule membranes.

The CD spectrum of reduced cytochrome (cyt.) beta-561 in chromaffin granule membranes resembles that of mitochondrial cyt. beta 1 and indicates possible heme-heme interaction in the protein. Based on spectroscopic data and analysis of the amino acid sequence, a model of cyt. beta-561 is suggested, in which the protein carries two transmembrane-localized hemes, each coordinated by two histidines. The model accounts for the presence of two different forms of cyt. beta-561 in chromaffin granule membranes and provides a mechanism of transmembrane electron transfer by this hemoprotein.