Cation Stimulation of the Proton-translocating Redox Activity at the Plasmalemma of Catharanthus Roseus Cells

Cultured Catharanthus roseus cells exhibit transmembrane ferricyanide reduction through a plasma membrane redox system which may be associated with proton translocation. Evidence shows that endogenous pyridine nucleotides serve as hydrogen donors for the reaction. The proton translocating function of the redox system is confirmed, in intact cells and isolated protoplasts, by the ability of Ca(2+) and other cations to increase both the redox activity and the efflux of protons. The role of the cations is seen to be not a simple general charge screening phenomenon as already described. By using ionic surfactants (CP(+), SDS(-)) it was shown that the net surface charge of the membrane can interact in the activation process via a cation attraction effect. It is proposed that specific binding of cations to the plasma membrane could alter the conformation of the redox system facilitating its interaction with NADH.