ELECTRON-TRANSFER CONSTITUENTS IN PLASMA-MEMBRANE FRACTIONS OF AVENA-SATIVA AND SACCHAROMYCES-CEREVISIAE

The presence of flavins, cytochromes and NAD(P)H dehydrogenase activities was investigated in plasma membrane preparations obtained from S. cerevisiae and from A. sativa roots. Those preparations contained, respectively, 280 and 216 pmol of non-covalently-bound flavin/mg protein. Both membrane fractions showed levels of NAD(P)H ferricyanide reductase activities which could not be accounted for by contaminating mitochondrial or endoplasmic reticulum dehydrogenases. While the yeast fraction lacked detectable hemoproteins, the plant preparation contained a cytochrome b-like pigment with absorption bands at 428.5, 530 and 560 nm in the room-temperature reduced-minus-oxidized difference spectrum. NADH could only reduce a small part of the cytochrome, which was also detected in an endoplasmic reticulum fraction from oat roots. No significant levels of cytochrome b5, P-450 and P-420 could be found in the oat preparations of plasma membranes and endoplasmic reticula.