Purification and Characterization of an Iminopeptidase from the Primary Leaf of Wheat (Triticum aestivum L.).

Iminopeptidase (EC 3.4.11.5) was substantially purified from the primary leaves of 7-day-old wheat seedlings (Triticum aestivum L.). The purification procedure consisted of five steps: acid precipitation, molecular exclusion chromatography on Sephacryl S-200, Ultrogel AcA 44, Sepharose 2B and ion-exchange chromatography on DEAE-cellulose. Iminopeptidase isolated in this manner was only active against the beta-naphthylamides of proline and hydroxyproline. For each substrate, the pH optimum was 7.4 and activity was sensitive to sulfhydryl group inhibitors. The iminopeptidase hydrolyzed the dipeptides Pro-Leu, Pro-Gly, Hyp-Gly, and Pro-Tyr. Iminopeptidase activity against the dipeptide Pro-Gly was higher than against Hyp-Gly. The molecular weight was estimated to be about 400,000. Evidence was obtained for the existence of endogenous inhibitors of iminopeptidase activity.