RAT-KIDNEY GLUTAMYL AMINOPEPTIDASE (AMINOPEPTIDASE-A) - MOLECULAR IDENTITY AND CELLULAR-LOCALIZATION

Glutamyl aminopeptidase [aminopeptidase A (EAP), EC 3.4.11.7] is an ec toenzyme that selectively hydrolyzes acidic amino acid residues from t he amino terminus of oligopeptides. EAP activity is highest within the kidney and small intestine. The murine pre-B cell BP-1/6C3 and the hu man kidney glycoprotein gp160 differentiation antigens have been repor ted to have biochemical properties indistinguishable from EAP. It is n ot known, however, if rat kidney EAP is a homologue of these antigens or molecularly distinct. Using the reverse transcription-polymerase ch ain reaction method with oligonucleotide primers based on the BP-1/6C3 nucleotide sequence, we isolated a 450-bp partial cDNA from rat kidne y poly(A)(+) RNA. The partial cDNA encoded a predicted protein that wa s 92% and 86% identical to the murine BP-1/6C3 and human gp160 antigen s, respectively; the amino acid sequence within the zinc-binding domai n was completely conserved. Purification of EAP from rat kidney and mi crosequence analysis of a tryptic digest peptide fragment (18-mer) ind icated that the fragment was highly similar to a region within the BP- 1/6C3 and gp160 proteins. Northern blot hybridization and immunoblot a nalyses were also consistent with labeling of products the same size a s reported for the BP-1/ 6C3 and gp160 antigens. There was a good corr elation between the cellular distribution of EAP mRNA and EAP immunore activity, with proximal tubules and glomerular mesangial cells having the highest densities. These results indicate that rat kidney EAP is a species homologue of the murine BP-1/6C3 and human gp160 antigens. Fu rthermore, on the basis of its cellular localization, rat kidney EAP i s likely to be involved in degradation of oligopeptides within the glo merulus and the glomerular filtrate. Since cells that express EAP also express receptors for angiotensin II, an intrarenal vasoactive hormon e that is a substrate for EAP, these results further suggest that EAP may play a role in modulating the activity of intrarenal angiotensin I I.