Dipeptidyl aminopeptidase IV and aminopeptidase P, two proline specific enzymes from the cytoplasm of guinea-pig brain: their role in metabolism of peptides containing consecutive prolines

In this study the majority of dipeptidyl aminopeptidase IV and aminopeptidase P activities of guinea-pig brain are reported to reside in the cytoplasm. Both activities were purified and soluble dipeptidyl aminopeptidase IV was found to have a relative molecular mass of 194 000 and to be comprised of two equal subunits of relative molecular mass 93 000 while native soluble aminopeptidase P had a relative molecular mass of 140 000. Both activities require proline or alanine in the penultimate position from the N-terminus. Dipeptidyl aminopeptidase IV removed the N-terminal dipeptide whereas aminopeptidase P removed only the N-terminal amino acid. Dipeptidyl aminopeptidase IV was inactive if proline was also present in the third position from the N-terminus whereas aminopeptidase P was unable to remove the N-terminal glycyl, pyroglutamyl or prolyl residues even though proline was present in the second position. Soluble dipeptidyl aminopeptidase IV was differentiated from the previously reported particulate form by its sensitivity to p-chloromercuribenzoate, N-ethyl maleimide and puromycin. The metabolism of Leu-Pro Pro-Ser by guinea-pig cytoplasm was investigated in the presence of inhibitors to evaluate the contribution by dipeptidyl aminopeptidase IV and aminopeptidase P to the hydrolysis of a peptide containing two consecutive proline residues. The results indicated that either dipeptidyl aminopeptidase IV or prolyl oligopeptidase were required along with aminopeptidase P and prolidase to achieve complete hydrolysis of this tetrapeptide. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.