The Insertion of Pig Microvillus Aminopeptidase into the Membrane as Probed by [125I]Iodonaphthylazide

Abstract

The insertion of pig intestinal microvillus aminopeptidase (EC 3.4.11.2) into the membrane was studied by the hydrophobic photolabel [125I]iodonaphthylazide. The aminopeptidase was either labeled in the microvillus membrane and purified, or labeled after detergent solubilization and purification in a buffer containing Triton X-100, and then isolated from the reaction mixture. Of the 3 subunits A (MW 162,000), B (MW 123,000) and C (MW 62,000) of the aminopeptidase, A and B but not C contained radioactivity, indicating that subunit A and B carry anchoring peptide. The radioactivity when released from the subunits by trypsin treatment was connected to low-MW material.