An essential arginine residue in vacuolar H+-ATPase purified from etiolated mung bean seedlings

Treatments of the tonoplast ATPase purified from mung bean seedlings (Vigna radiata L.) with guanidino modifiers, phenylglyoxal and 2,3-butanedione, caused a marked loss of the ATP hydrolysis activity and proton translocation in a concentration-dependent manner. Kinetic analysis yielded first order rate constants, k(2), of 0.416 and 0.227 s(-1) and steady-state dissociation constants, K-i, of 19.3 and 24.2 mM for phenylglyoxal- and butanedione-inhibition of vacuolar H+-ATPase, respectively. The reaction order of phenylglyoxal- and butanedione-inhibition was calculated to be 0.94 and 0.89, respectively, suggesting that at least one arginine residue of vacuolar H+-ATPase was modified by both reagents. Lineweaver-Burk plots showed that the mode of inhibition of vacuolar H+-ATPase by both modifiers is competitive. Mg-ATP, the physiological substrate of vacuolar H+-ATPase, but not its analogs, exerted preferentially partial protection against phenylglyoxal and butanedione, indicating that the arginine residue involved in the inhibition of enzymatic activity may be located at or near the active site and directly participate in the binding of the substrate.