Fractionation and characterization of oxytocinases in human semen

Two isoenzymes of oxytocinase activity were fractionated from human seminal plasma by acrylamide-agarose gel chromatography and partly characterized using S-benzyl-L-cysteine-p-nitroanilide (BCN) and L-leucine-p-nitroanilide (LN) separately as substrates. These isoenzymes appeared to be metallo-aminopeptidases with different elution volumes (90 ml and 150 ml), apparent molecular weights (unknown value and 300,000) and pH optima (6.8 and 7.0 with BCN and 7.2 and 7.4 with LN), but with similar substrate affinity and thermal sensitivity, and susceptibility to EDTA, divalent metal ions, L-methionine, polypeptide hormones and prostaglandins. A comparison of the enzymic properties with pregnancy-associated oxytocinases suggests that seminal oxytocinases are related more closely to amniotic fluid isoenzymes than to pregnancy serum, placental and uterine isoenzymes.