Comparison of the vacuolar membrane ATPase of Neurospora crassa with the mitochondrial and plasma membrane ATPases.

The vacuolar membrane ATPase of Neurospora crassa closely resembles the mitochondrial ATPase in its substrate specificity, substrate affinity, and sensitivity to the inhibitor N,N'-dicyclohexylcarbodiimide. Three different mutants with altered mitochondrial ATPase activity, exhibited as 1) resistance to N,N'-dicyclohexylcarbodiimide, 2) enhanced sensitivity to N,N'-dicyclohexylcarbodiimide, and 3) very low specific activity, were found to be unaltered in the vacuolar membrane ATPase. The vacuolar membrane ATPase was similar to the mitochondrial ATPase and approximately 10-fold more sensitive than the plasma membrane ATPase in its sensitivity to the inhibitors 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole, 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate, and 5'-adenylylimidodiphosphate. By contrast, the vacuolar ATPase resembled the plasma membrane ATPase in its response to quercetin (both 10-fold more sensitive than the mitochondrial ATPase); it was unique in its sensitivity to KNO3. A N,N'-dicyclohexylcarbodiimide-binding protein, migrating between molecular weight markers of 14,400 and 21,500, was identified as a putative component of the vacuolar membrane ATPase. Taken together, these findings support the argument that the vacuolar membrane ATPase is a distinct enzyme, more like the mitochondrial F0F1 ATPase than the plasma membrane ATPase.