Plasma Membrane Cytochrome Components: Midpoint Redoxpotentials, Light- and NADH Mediated Reductions
The thorough characterization of PM redox components is highly dependent on the method for isolation and purity of the membranes. The purity and cytochrome content of PM fractions from several plant species, obtained by aqueous two phase partitioning, was investigated. Preparations are generally enriched in vanadate-sensitive ATPase activity (PM marker) and show strongly decreased (6 to 50 fold) levels of NADH-CCR activity (presumptive ER marker). The remaining activity might originate from specific PM redox constituents. Variable amounts of latent IDPase activity (Golgi marker) were detected. PM preparations oxidize NADH (in piesenye of duroquinone and KCN) at rates between 9 and 40 nmol NADH.min−1.mg−1 protein. Triton X-100 stimulation indicates the presence of tightly sealed right-side out PM vesicles.