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Rice bifunctional alpha-amylase/subtilisin inhibitor: characterization, localization, and changes in developing and
H Yamagata1, K Kunimatsu, H Kamasaka
1Laboratory of Biochemistry, Faculty of Agriculture, Kobe University, Japan.
Abstract:
A bifunctional alpha-amylase/subtilisin inhibitor (RASI) was purified to electrophoretic homogeneity from rice (Oryza sativa L.) bran. Its molecular mass was 21 kDa by SDS-PAGE and its isoelectric point was 9.05. Purified RASI inhibited subtilisin Carlsberg strongly and inhibited alpha-amylase from germinating rice seeds weakly. It inhibited rice alpha-amylase more than barley alpha-amylase, and the inhibition of rice alpha-amylase was greater at higher pHs. RASI did not inhibit trypsin, chymotrypsin, cucumisin, or mammalian alpha-amylase. The RASI was in the outermost part of the rice grain and its subcellular site seemed to be aleurone particles in aleurone cells. SDS-PAGE and western blotting showed that RASI was synthesized in the late milky stage in developing seeds, and it remained fairly constant during the first 7 days of germination.