p‐NITROPHENYL PHOSPHATASES OF A MEMBRANE FRACTION FROM BOVINE CEREBRAL CORTEX

Three different types of p‐nitrophenyl phosphatases (NPPases) were solubilized by deoxycholate treatment from a membrane fraction of bovine cerebral cortex, and their characteristics were determined. Of these three NPPases (acid, Mg2+‐activated, and K+, Mg2+‐activated), only K‐Mg NPPase was stimulated about two‐fold by phospholipid and was inhibited by unsaturated neutral lipids and fatty acids. Unlike Na+‐K+‐Mga+‐activated ATPase, the enzyme did not absolutely require phospholipid for its activity, but was similarly thermolabile and was protected by phospholipid from thermal inactivation. Acid NPPase was separable from the other two NPPases by ammonium sulphate fractionation, and partly solubilized by dialysis against ATP‐mercaptoethanol solution. Hg2+ inhibited equally all three NPPases, but Ca2+ inhibited only Mg and K‐Mg NPPases. Ouabain was effective on K‐Mg NPPase alone.