CORN CYSTATIN-I EXPRESSED IN ESCHERICHIA-COLI - INVESTIGATION OF ITS INHIBITORY PROFILE AND OCCURRENCE IN CORN KERNELS

Corn cystatin I was expressed in Escherichia coli as a mature protein. It was purified by gel filtration on Sephadex G-50, ion-exchange HPLC, and reversed-phase HPLC. The purified protein showed strong inhibitory activities against papain (K-i : 3.7 X 10(-8) M), and cathepsins H (K-i: 5.7 X 10(-9) M) and L (K-i: 1.7 X 10(-8) M), whereas it inhibited cathepsin B to a lesser extent (K-i: 2.9 X 10(-7) M). Western blot analysis using antibody raised against corn cystatin I revealed that in the corn kernel, the protein occurs with a molecular mass of approximately 13 kDa. Localization in the aleurone layer and embryo of the corn kernel was shown by immunostaining microscopy.