Radiation inactivation analysis of H+-pyrophosphatase from submitochondrial particles of etiolated mung bean seedlings

Radiation inactivation analysis was employed to determine the functional ma sses of enzymatic activity and proton translocation of H+-pyrophosphatase f rom submitochondrial particles of etiolated mung bean seedlings. The activi ties of H+-pyrophosphatase decayed as a simple exponential function with re spect to radiation dosage, D-37 values of 6.9+/-0.3 and 7.5 +/- 0.5 Mrad we re obtained for pyrophosphate hydrolysis and its associated proton transloc ation, yielding molecular masses of 170+/-7 and 156+/-11 kDa, respectively. In the presence of valinomycin and 50 mM KCl, the functional size of H+-py rophosphatase of tonoplast was decreased, while that of submitochondrial pa rticles remained the same, indicating that they are two distinct types of p roton pump using PPi as their energy source. (C) 2000 Federation of Europea n Biochemical Societies.