Characterization of the phosphorylated intermediate of the K+-ouabain-insensitive ATPase of the rabbit colon brush-border membrane.

ABSTRACT

The rabbit colon brush-border membrane possesses a unique K+-stimulated, ouabain-insensitive ATPase. This enzyme is similar to previously described potassium-transporting enzymes such as the ubiquitous (Na + K)-ATPase and the gastric (H+ + K+)-ATPase in forming a phosphorylated intermediate whose rate of dephosphorylation is accelerated by K+. The molecular weight of the phosphorylated polypeptide subunit of the colon membrane enzyme is 114,000 as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The release of 32Pi from the 32P-labeled ATPase at alkaline pH and in the presence of hydroxylamine at pH 5.0 suggests that the phosphorylated enzyme intermediate is an acyl phosphate. These results indicate that the phosphorylated intermediate of the colon brush-border membrane is similar in chemical nature and molecular weight to the phosphorylated intermediates of other cation-transporting ATPases.