EFFECTS OF DIVALENT-CATIONS ON NADH-LINKED ELECTRON-TRANSFER IN CORN ROOT PLASMA-MEMBRANE

The effects of calcium (Ca2+), cadmium (Cd2+), and copper (Cu2+) catio ns on NADH-linked electron transfer in corn root plasma membrane vesic les were investigated. The reduction of both cytochrome c and ferricya nide were slightly stimulated by Ca2+ but not significantly affected b y Cd2+. However, Cd2+ induced a redox-linked increase in light scatter ing suggesting an increase in the size/volume of the vesicles. The pre sence of micromolar levels of Cu2+ decreased the reduction rates of bo th cytochrome c and ferricyanide. However, in contrast to ferricyanide reduction, Cu inhibition to the cytochrome (c) under bar reduction wa s more effective and was less sensitive to ionic strength. Copper inhi bition changed the Michaelis-Menten dependence of the ferricyanide red uction but not that of cytochrome (c) under bar. These results suggest that the reduction of cytochrome (c) under bar and ferricyanide must occur at different membrane sites.