A preliminary study of the protease activities in germinating brown rice (Oryza sativa L.)

Abstract

Proteases hydrolyse storage proteins to provide precursors for perpetuating species. The aim of this study was to investigate and characterise different proteases in germinating brown rice. The protease activity of brown rice increased sevenfold during 7 days of germination. It was highest on day 6 when determined at pH 3.5. With casein as substrate the proteases showed two catalytic groups: acidic proteases with an optimal pH of 3.5 and alkaline proteases with an optimal pH of 8.0. The acidic protease activity was inhibited by Ba(2+) and Pb(2+) but stimulated by Zn(2+) , while the alkaline protease activity was inhibited by Ca(2+) and Pb(2+) but stimulated by Mg(2+) and Zn(2+) . SDS-gelatin-PAGE assay showed two protease activity bands at pH 3.5, while two different bands with higher molecular weights were observed at pH 8.0. Inhibition assay revealed that pepstatin A and E-64 inhibited 67.63 and 38.26% respectively of the protease activity at pH 3.5, indicating the presence of aspartic and cysteine proteases. Metalloproteases played a major role under alkaline conditions (88.37% inhibition with EDTA). Germinated brown rice proteases fall into different classes with different properties. This study is helpful for their further purification.