Uteri of pregnant and nonpregnant women contain enzymic activities which inactivate oxytocin. A potent enzyme, which has been partially purified from uterine homogenates, cleaves the prolyl-leucyl peptide bond of oxytocin. This findinig associates for the first time the release of the dipeptide leucylglycinamide with the degradation of neurohypophyseal hormones.

Peptidases which are specific for proline residues have been described and include endopeptidases (post-proline cleaving enzyme and proline specific endopeptidase), N-terminal exopeptidases (post-proline dipeptidyl aminopeptidase, proline iminopeptidase, aminopeptidase P), C-terminal exopeptidases (prolylcarboxypeptidase, and carboxypeptidase P) and dipeptidases (prolyl dipeptidase and proline dipeptidase). The properties, distinguishing charcteristics, and possible significance of these proline specific endo- and exopeptidases are discussed. In addition, reference is made to a series of enzymes which can hydrolyze proline containing peptide bonds, but which are not specific for proline.

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