Topological studies on the hydrolases bound to the intestinal brush border membrane. I. Solubilization by papain and Triton X-100.

Papain digestion of closed, right side out vesicles from pig, rat and rabbit jejunum brush border induces the release of the hydrolases bound to the membrane without grossly affecting the lipid bilayer limiting the vesicles. This observation definitely proves that intestinal hydrolases are surface components attached to the external side of the membrane. All proteins released by papain could be identified by electrophoresis and immunoelectrophoresis to already known intestinal hydrolases, with the exception of an unidentified substance strongly stained by the Schiff's reagent. The early observation that the aminopeptidase form released from pig bursh border by Triton X-100 is different from that released by papain was extended to other hydrolases from pig, rat and rabbit. In some cases, the Triton-released form could be converted by further proteolytic digestion into a new form similar to that liberated by papin. These facts may be related to the existence of hydrophobic anchors retaining the intestinal hydrolases to the membrane surface.