Cystine Aminopeptidase and Oxytocinase Activity in Pregnancy: A Comparative study in Human and Rat Tissues

Fractionation and characterization of cystine aminopeptidase (oxytocinase) and arylamidase of the human placenta

“…Homogenates of human placenta inactivate oxytocin hormone (Hawker, 1956;Ryden, 1966). It has been confirmed that the inactivation is enzymic in nature.…”

“…6, the molecular weights for the placental enzymes were 309 000 for cystine aminopeptidase I and arylamidase I, and 76 400 for cystine amino¬ peptidase II. Ryden (1966) has shown that at least two different enzyme systems in human placenta are able to split oxytocin and CysNA. With human placental extract he found that the biological and synthetic substrates were split with pH optima at 6-0-6-2 and 7-2-7-3 and the activity at pH 7-3 was higher than that of the enzyme at pH 6-0.…”

Fractionation and characterization of oxytocinases in human semen

“…The enzyme also has the ability to inactivate vasopressin and angiotensin II and so appears to have a broad specificity, hydrolysing aromatic neutral, basic and acidic N-terminal amino acids from the octapeptides (Tuppy, 1961; Ryden, 1966;Sjoholm & Yman, 1967;Mizutani et ai, 1979). It also splits the equivalent amide bonds in a number of synthetic peptides; the substrate behaviour of these peptides is similar to that of oxytocin (Tuppy, 1961; Ryden, 1966;Floyd et ai, 1973;Tovey et ai, 1973;Small & Watkins, 1974, 1975Mizutani et ai, 1979).…”

“…The enzyme also has the ability to inactivate vasopressin and angiotensin II and so appears to have a broad specificity, hydrolysing aromatic neutral, basic and acidic N-terminal amino acids from the octapeptides (Tuppy, 1961; Ryden, 1966;Sjoholm & Yman, 1967;Mizutani et ai, 1979). It also splits the equivalent amide bonds in a number of synthetic peptides; the substrate behaviour of these peptides is similar to that of oxytocin (Tuppy, 1961; Ryden, 1966;Floyd et ai, 1973;Tovey et ai, 1973;Small & Watkins, 1974, 1975Mizutani et ai, 1979). The activity of oxytocinase which appears in the maternal circulation soon after conception and then increases progressively with gestational age is believed to be involved in both maintenance and termination of human pregnancy (Roy & Karim, 1983;Roy et ai, 1985aRoy et ai, , b, 1986aYeang, 1986).…”

“…Oxytocinase (EC 3.4.11.3), a pregnancy-specific -aminoacyl hydrolase, cleaves the pentapeptide ring of the octapeptide neurohypophysial oxytocic hormone, oxytocin between the amino-terminal cysteine and penultimate tyrosine, and hence is also called cystine aminopeptidase (Tuppy, 1961;Ryden, 1966). The enzyme also has the ability to inactivate vasopressin and angiotensin II and so appears to have a broad specificity, hydrolysing aromatic neutral, basic and acidic N-terminal amino acids from the octapeptides (Tuppy, 1961; Ryden, 1966;Sjoholm & Yman, 1967;Mizutani et ai, 1979).…”