Some properties of a cysteine proteinase inhibitor from corn endosperm.

Thougha numberof proteinaceous cysteine proteinase inhibitors (cystatins) of animal origin have long been studied in detail,1* little is well-defined about plant cystatins except for oryzacystatins from rice seeds.2'3) Preceding the studies on oryzacystatins, however, we purified a cysteine proteinase inhibitor from corn.4'5) In this study we carried out amino acid analysis and kinetic studies on this inhibitor as a corn cystatin and also tried to comparethe results of the studies with those obtained with oryzacystatins. Inhibitory activities against cysteine proteinases were measured either by the method using benzoylarginine />-nitroanilide (BAPA)5) or by that using benzoylarginine /?-naphthylamide (BANA). Using the BANAmethod, inhibited proteinase activity was measured as follows: 0.1ml of 0.5m sodium phosphate buffer (pH 6.0)