Dipeptidyl-aminopeptidase III of rat brain. Selective affinity for enkephalin and angiotensin

The cytosolic dipeptidyl-aminopeptidase III (EC 3.4.14.4) from rat brain was partially purified using Arg-Arg-4-methoxy-beta-naphthylamide as a substrate. It was completely separated from aminopeptidase B on DEAE-Sephacel ion exchange chromatography. Similar to bovine pituitary dipeptidyl-aminopeptidase III, it has a pH optimum of 9, prefers Arg-Arg-4-methoxy-beta-naphthylamide as a substrate, and catalyzes the sequential release of dipeptides from the NH2 terminus of peptide substrates provided they are not smaller than a tetrapeptide. Among numerous biologically active peptides tested, angiotensins and enkephalins were the most preferred substrates with micromolar affinities, suggesting that dipeptidyl-aminopeptidase III may play a physiologic role in regulating enkephalin and/or angiotensin disposition.