Abstract: The plasma membrane vesicles were purified from soybean ( Glycine max L. ) hypocotyls by two-phase partitioning methods. The stimulatory effects of K+ on the coupling between ATP hydrolysis and proton transport by the plasma membrane H+-ATPase were studied. The results showed that the proton transport activity was increased by 850% in the presence of 100 mmol/L KC1, while ATP hydrolytic activity was only increased by 28.2%. Kinetic studies showed that Km of ATP hydrolysis decreased from 1.14 to 0.7 mmol/L, while Vmax of ATP hydrolysis increased from 285.7 to 344.8 nmol Pi·mg- l protein·min-1 in the presence of KC1. Experiments showed that the optimum pH was 6.5 and 6.0 in the presence and absence of KC1, respectively. Further studies revealed that K+ could promote the inhibitory effects of hydroxylamines and vanadates on the ATP hydrolytic activity. The above results suggested that K+ could regulate the coupling between ATP hydrolysis and proton transport of the plasma membrane H+ -ATPase through modulating the structure and function of the kinase and phosphatase domains of the plasma membrane H + -ATPase.

Key words: Soybean hypocotyl, Plasma membrane H+-ATPase, K+ , ATP hydrolysis, Proton transport, Coupling