Studies on ox brain aminopeptidases.

1. Mn(2+)-inhibited and Mn(2+)-activated aminopeptidases have been observed in ox brain and separated from one another by DEAE-cellulose column chromatography. 2. The Mn(2+)-inhibited enzyme has been purified 36-fold; it exhibits a specificity for tripeptide substrates, whereas the Mn(2+)-activated aminopeptidase cleaves dipeptides as well as tripeptides. 3. Ammonium sulphate treatment generates a Mn(2+)-stimulated aminopeptidase that is stable to dialysis against EDTA and water, in contrast with an endogenous Mn(2+)-activated preparation that is irreversibly denatured by such dialysis against EDTA and water.