Ectoenzymes of the kidney microvillar membrane. Aminopeptidase P is anchored by a glycosyl-phosphatidylinositol moiety.

The mode of membrane anchorage of three kidney microvillar membrane ectoenzymes has been examined. The release of aminopeptidase P (EC 3.4.11.9) from kidney membranes by bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) and the pattern of detergent solubilization of this ectoenzyme implies that it is anchored to the membrane via a covalently attached glycosyl-phosphatidylinositol moiety. As deduced by phase separation in Triton X-114, octyl-glucoside solubilized the amphipathic form of aminopeptidase P, whereas the PI-PLC-released form displayed hydrophilic properties. In contrast, the pattern of detergent solubilization of two microvillar carboxypeptidases and their resistance to release from the membrane by bacterial PI-PLC suggest that these two ectoenzymes are not anchored via phosphatidylinositol.