Widespread tissue distribution of aminopeptidase A, an evolutionarily conserved ectoenzyme recognized by the BP‐1 antibody

Early B-lineage cells in mice express a cell surface glycoprotein, recognized by the BP-1 and 6C3 monoclonal antibodies, that has been identified as aminopeptidase A (APA E.C.3.4.11.7). In the present studies we obtained evidence by DNA "zoo-blot" analysis that the APA gene is highly conserved. This ectoenzyme catalyzes the removal of N-terminal Glu- and Asp-residues to convert angiotensin II to angiotensin III, a degradation step important in local regulation of blood pressure in mammals. To gain further insight into the physiology of this molecule, which is shared between immune and vascular systems, we examined the tissue distribution of BP-1 mRNA using a cDNA probe and of the protein antigen using the BP-1 antibody for immunohistology. APA transcripts were present in all tissues examined. Abundant BP-1/APA was found in the intestinal brush border of the small intestine, renal glomeruli, proximal renal tubules, pulmonary alveolar walls and vascular endothelium in many organs. Other tissues containing the BP-1 antigen included stromal cells in the thymus cortex, bile canaliculi in liver, gall bladder epithelium, interlobular ducts in pancreas, the ovarian theca interna, basement membrane of the epididymis and the splanchnopleure in placenta. APA enzyme activities have been identified in most of these locations, in keeping with identification of the BP-1/6C3 antigen as APA. The data suggest this ectopeptidase may serve diverse physiologic roles in a broad spectrum of tissues.