ON THE QUESTION OF THE IDENTITY OF CYTOCHROME-B-560 IN THYLAKOID STROMAL MEMBRANES

Stromal membranes enriched in PS I contain a low potential cytochrome with a reduced alpha-band peak close to 560 nm. The identity of this c ytochrome component has been ascribed either to a low potential form o f the Photosystem II cytochrome b-559 or to a different cytochrome wit h a reduced alpha-band of 560 nm. The half-bandwidth of the 560 nm com ponent in stromal membranes is identical to that of purified cytochrom e b-559. Western blots show that the stromal membranes contain an amou nt of PS II cytochrome b-559 alpha-subunit that is more than sufficien t to account for the cytochrome b-560 detected spectrophotometrically in these membranes. These immunochemical data and the similarity of (i ) the spectral peaks, and (ii) the redox properties of low potential P S II cytochrome b-559 and the b-560 component, suggest that the simple st inference is that the cytochrome b-560 protein in stromal membranes is identical to the PS II cytochrome b-559.