Purification and inhibition by neuropeptides of angiotensin-converting enzyme from rat brain

Angiotensin-converting enzyme was solubilized with papain from a particulate fraction of rat brain and purified to apparent homogeneity by a procedure including DEAE-cellulose, hydroxylapatite, Sephadex G-200, Cys(Bzl)-Pro-Sepharose, and ricin-Sepharose chromatography. Bradykinin potentiators, SQ 14,225, and Arg-Pro-Pro strongly inhibited the activity of the purified enzyme, whereas Phe-Ala, phosphoramidon, and pentobarbital exerted little inhibitory effect on the activity. Among neuropeptides investigated, substance P, bradykinin, and Leu-enkephalin (Arg6) exerted strong inhibitory actions on the enzyme. Furthermore, the latter two peptides were shown to be good substrates for the enzyme. Thus, angiotensin-converting enzyme of rat brain is distinct from endogenous enkephalinase and may interact with various neuropeptides located in the brain.