Proton-Translocating Inorganic Pyrophosphatase in Red Beet (Beta vulgaris L.) Tonoplast Vesicles

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Abstract
The substrate and ionic requirements of ATP and inorganic pyrophosphate (PPi) hydrolysis by tonoplast vesicles isolated from storage tissue of red beet (Beta vulgaris L.) were compared with the requirements of ATP-and PPi-dependent proton translocation by the same material. Both ATP hydrolysis and ATP-dependent proton translocation are most stimulated by Cl− and inhibited by NO3−. NaCl and KCl support similar rates of ATP hydrolysis and ATP-dependent proton translocation while K2SO4 supports lesser rates for both. PPi hydrolysis and PPi-dependent proton translocation are most stimulated by K+. KCl and K2SO4 support similar rates of PPi hydrolysis and PPi-dependent proton translocation but NaCl has only a small stimulatory effect on both. Since PPi does not inhibit ATP hydrolysis and ATP does not interfere with PPi hydrolysis, it is inferred that the two phosphohydrolase and proton translocation activities are mediated by different tonoplast-associated enzymes. The results indicate the presence of an energy-conserving proton-translocating pyrophosphatase in the tonoplast of red beet.