Summary: Triton X-100 (TX-100) extraction of plasma membrane solubilized two types of ATPase differing in their pH of maximum activity. The activity measured at pH 8°5 was inhibited by vanadate and the activity measured at pH 6°5 was not. The vanadate-sensitive ATPase had a relatively basic isoelectric point (8°65) and therefore could be separated from the vanadate-insensitive ATPase using chromatofocusing. Elution of the TX-100 membrane extract in a pH gradient from 9 to 6 generated two peaks of ATPase activity: one in the acidic range, composed of an FF-type ATPase, and one in the basic range, corresponding to the vanadate-sensitive activity. Electrophoretic analysis of proteins from the latter peak revealed one major polypeptide of 37 kDa. This peptide was shown to correspond to spot A37 in a two-dimensional protein map of . Using the gene for the -operon of as a probe in heterologous hybridization, sequences were detected in the genomic DNA of , suggesting that a gene coding for an enzyme related to this P-type ATPase is present in the genome. We therefore postulate the presense of two distinct kinds of ATPase in : one of the F-type which is resistant to vanadate inhibition, and one, probably of the P-type, which is vanadate-sensitive.


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