Partial purification and specificity of iminodipeptidase.

Grassmann et al. (1,2) ascribed the hydrolysis of prolylglycine and prolylglycylglycine to an enzyme which they named prolinase. Johnson (3) questioned the existence of an enzyme specific for proline peptides since partially purified preparations of aminopeptidase could hydrolyze prolylglycylglycine. More recently Neuman and Smith (4) demonstrated that an enzyme in swine kidney could hydrolyze prolyl and hydroxyprolyl dipeptides, and that the enzyme is activated by cadmium ion as well as by manganous ion. This extremely labile enzyme has now been purified 30-fold. Specificity studies demonstrate that the action of the purified enzyme is restricted to dipeptides which possess the free imino group of proline or hydroxyproline. The enzyme has no action on amides of these imino acids or on the tripeptides, L-prolylglycylglycine, hydroxy-L-prolylglycylglycine, and glycyl-Lprolylg1ycine.l In view of the restricted specificity of this enzyme, we are naming it iminodipeptidase. The older name, prolinase, which indicates a much more general action, is inappropriate and misleading. The synthesis of several new diand tripeptides containing L-proline and hydroxy+proline is described.