Fractionation of cystine aminopeptidases ('oxytocinase') from term human placenta and maternal serum.

Cystine aminopeptidase (EC 3.4.11.3) enzymes, present in term human placenta and maternal serum, were compared with respect to their behaviour on ion-exchange columns, Km and pH optima, chelator, metal ion and L-methionine effects, Sepharose 6B elution profiles and molecular weights. From placental extracts two activity peaks (CAS I and II) hydrolysing S-benzyl L-cysteine paranitroanilide were separated on DEAE Sephacel. Differences in properties between the two forms were evident. Maternal serum enzyme eluted from the DEAE Sephacel column in a position similar to that of placental CAS I. In addition, the maternal serum enzyme was similar in properties to placental CAS I. It is possible that of all the different cystyl aminopeptidase enzyme systems present in placental tissue, only one appears in maternal blood.