Partial purification and characterization of an anion-activated ATPase from radish microsomes

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Abstract
Previous investigation showed two distinct ATP‐dependent proton‐transporting systems in microsomal vesicle from radish seedlings, one inhibited by vanadate and one inhibited by NO−3 [1]. On the bases of the effects of these inhibitors we could discriminate two distinct ATPase activities in the same material. The NO−3‐sensitive activity was separated from the vanadate‐sensitive activity and partially purified by a single‐step chromatographic method, which lead to approx 35‐fold purification from the microsomes and to a specific activity of 2.3 μmol Pi× min−1× mg protein−1, at 30°C. The partially purified activity was specific for ATP, some activity being observed toward GTP, and even less toward CTP, UTP and ITP. No significant Pi hydrolysis was found with ADP, AMP, p‐nitrophenylphosphate and glucose 6‐phosphate. ADP but not AMP was inhibiting in the presence of ATP. The activity was dependent on divalent cations in the order of preference: Mg2+ > Mn2+ > Co2+ > Ca2+ > Zn2+. The activity was unaffected by monovalent cations, strongly activated by Cl−, inhibited by 90% by 50 mM NO−3, virtually unaffected by oligomycin and NaN3. At least 90% of the activity was abolished in the presence of each: 10 μM N,N′‐dicyclohexylcarbodiimide, 10 μM erythrosin B, 10 μ mersalyl, 100 μM trimethyltin, 100 μM diethylstilbestrol, 100 μM N‐ethylmaleimide. No inhibition has been found in the presence of Ca2+, at a concentration blocking the vanadate‐sensitive activity. Nigericin, gramicidin and carbonylcyanide p‐trifluoromethoxyphenylhydrazone stimulated the activity of this preparation after it was incubated in the presence of sonicated phospholipids, suggesting the capacity of the ATPase to function as a H+ ‐transporting system. All characteristics mentioned were closely similar to those described in the vacuolar ATPases.