Regulatory effects of adenosine diphosphate on the activity of the plasma membrane ATPase of corn roots.

Plasma membrane enriched microsomal fraction was isolated from corn root cells by sucrose density centrifugation. The ATPase activity as measured by the release rate of inorganic phosphate, was decreased by the presence of modifiers which included diethylstilbestrol, vanadate, N,N'-dicyclohexylcarbodiimide, and miconazole. The presence of ADP also decreased the rate of ATP hydrolysis. Furthermore, a preincubation of the membrane with ADP significantly reduced the inhibitory effects of these membrane ATPase modifiers. Since the modes of interaction of these modifiers with the enzyme are different, the results suggest that the binding of ADP may stabilize the plasma membrane ATPase in a modifier insensitive state.