The detergent form of the major aminopeptidase from the plasma membrane of midgut caeca cells of Rhynchosciara americana (Diptera) larva

Abstract

1. 1. Plasma membrane-bound aminopeptidases from Rhynchosciara americana midgut caeca cells may be solubilized by Triton X-100 or may be released by papain treatment. 2. 2. The major detergent solubilized aminopeptidase was purified by electrophoresis and was shown to have M r 169,000 and pI 7.8. 3. 3. K m values for two substrates ( l-arginine -p- nitroanilide and l-leucine -p- nitroanilide ) and K i values for four linear inhibitors (arginine hydroxamate, leucine hydroxamate, hydroxyl amine and isoamyl alcohol) corresponding to the major detergent-solubilized aminopeptidase are identical to those of the major papain released aminopeptidase, which was previously purified and characterized. 4. 4. Both aminopeptidase forms display the same pH optimum (7.2 in Tris-HCl buffer) and follow the same thermal inactivation kinetics (half-lives of 23 min at 50°C). 5. 5. Treatment of the major detergent form of the aminopeptidase with papain results in the appearance of a M r 97,000 aminopeptidase. 6. 6. The data support the proposal that the papain-form of the aminopeptidase (M r 207,000) results from the dimerization of the products of the papain action upon the major native (M r 169,000) aminopeptidase.