Purification of three aminopeptidases from human maternal serum

1. 1. Three aminopeptidases (I-III) were purified from maternal serum using sequential chromatographie fractionations. 2. 2. Aminopeptidase I was specific for N-terminal α- l-dicarboxylic acid residues and activated by alkaline earth metals (Ba 2+. Ca 2+. Sr 2+). It is concluded that aminopeptidase I is aminopeptidasc A ( l-α-aspartyl-( l-α-glutamyl)-peptide hydrolase, EC 3.4.11.7). 3. 3. Aminopeptidase II hydrolysed all tested substrates including l-cystine and Bz- l-cysteine derivatives but preferred l-leucine derivatives. The properties of aminopeptidase II are equal to those described for the cystine aminopeptidase (oxytocinase) (EC 3.4.11.3.). 4. 4. Aminopeptidase III preferred l-alanine derivatives as substrates. It was activated by Co 2+, but strongly inhibited by amastatin. puromycin and l-methionine. The characteristics are reminiscent of those of alanine aminopeptidase (EC 3.4.11.-).