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

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 labelled in the microvillus membrane and purified, or labelled after detergent solubilization and purification in a buffer containing Triton X-100, and then isolated from the reaction mixture. Of the three subunits A (Mr 162000), B (Mr 123000) and C (Mr 62000) of the aminopeptidase, A and B, but not C contained radioactivity, indicating that both subunit A and B carry anchoring peptide. The radioactivity when released from the subunits by trypsin treatment was connected to low-molecular-weight material.