PROBABLE LACK OF FUNCTION OF C-TYPE CYTOCHROME IN THE PHOTOSYNTHETIC SYSTEM OF THE BLUE-GREEN-ALGA ANABAENA-VARIABILIS

Quantitative study of the cytochrome c acting in the photosynthetic system of the blue-green alga Anabaena variabilis (M-2) was done with membrane fragments and intact cells.Membrane fragments highly active in the NADP+-Hill reaction (above 200 μmoles/mg chl.a;-hr) retained photoresponsive cytochrome c equal only one-tenth that of P700, while the plastocyanin content was almost equal to that of P700. The cytochrome content in intact cells was a little larger than that in membrane fragments on the chlorophyll a basis. However, the values relative to P700 (1/9) and plastocyanin (1/10) were identical with those in membrane fragments. The content was also far smaller than that of reaction center II's (1/6). If the cytochrome mediates all electrons from reaction center II, the cytochrome oxidation-reduction should have a rate constant of 2.4×102 sec-1 which is one order above of the rate constant of the cytochrome reduction (2.3 to 3.5×101sec-1). These quantitative relationships indicate that in Anabaena variabilis (M-2), c-type cytochrome, either cytochrome f or algal cytochrome c, cannot function in the main electron flow between two reaction centers. © 1979 Oxford University Press.