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Articles

Purification and Characterization of an Iminopeptidase from the Primary Leaf of Wheat (Triticum aestivum L.) ¹

Plant Sciences Section, School of Agriculture and Forestry, University of Melbourne, Parkville, Victoria 3052, Australia

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 -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.

³ To whom reprint requests should be addressed.

¹ Supported by grants to M. J. D. from the Wheat Industry Research Council of Australia and the Australian Research Grants Scheme. During the course of this study, S. P. W. held a Commonwealth Postgraduate Research Award.

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