Comparison of the Properties of Plasma Membrane‐Bound and Mitochondria‐Bound ATPases in the Yeast Schizosaccharomyces pombe

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Abstract
Two distinct membrane‐bound ATPases of the glucose‐grown yeast Schizosaccharomyces pombe are separated by differential and isopycnic gradient centrifugation. The mitochondrial ATPase, with optimal activity at pH 9.0, equilibrates with cytochrome c oxidase at densities 1.17 and 1.19 g × cm−3 while the non‐mitochondrial ATPase, with optimal activity at pH 6.0 is associated with mannans in 1.21‐g × cm−3 particles. Cytochemical staining for carbohydrates confirms the plasma membrane origin of vesicles found in a subcellular fraction enriched about 10 times in pH‐6.0 ATPase activity. The following analogies are found between the two purified membrane‐bound ATPases. They hydrolyse preferentially ATP and require magnesium. They exhibit a Km of 3.3 mM for ATP‐Mg at pH 6.0. The two activities are inhibited by ADP, Dio‐9, dicyclohexylcarbodiimide, triethyltin, miconazole, sodium fluoride and p‐hydroxymercuribenzoate. Nevertheless, the plasma membrane‐bound ATPase is distinct from the mitochondria‐bound ATPase in the following properties. The plasma membrane‐bound ATPase is not sensitive to the antibody dressed against the purified mitochondrial enzyme. Excess of Mg2+ inhibits the mitochondria‐bound ATPase but not the plasma membrane one. The relative specificities for nucleoside triphosphates and cations of the two enzymes are different. In contrast to the mitochondrial enzyme, the plasma membrane‐bound ATPase is not stimulated by carbonate and maleate anions. The plasma membrane‐bound ATPase is not inhibited by the mitochondrial inhibitors oligomycin and venturicidin.

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