Distribution and characterization of enzymes causing starch degradation inrice (Oryza sativa cv. Koshihikari)

The thermal dependency and stability of enzymes producing reducing sugar (R S) were examined in bran, the exterior 13% part (outer endosperm), and the remaining inner endosperm of rice grains. RS-producing enzymes in the inner endosperm showed a higher optimum temperature than those in other parts of the rice grain. Diethylaminoethyl-Sephacel chromatography of crude extract s revealed two peaks of RS-producing activity with different optimum temper atures (60 and 37 degrees C) in all three parts, alpha-Glucosidase (EC 3.2. 1.20) and alpha-amylase (EC 3.2.1.1) isoform G were thought to be major com ponents of the RS-producing activities with high and low optimum temperatur es, respectively. The peak with a high optimum temperature was a more abund ant component in the inner endosperm, compared with other parts of the rice grain. Thus, different parts of rice were found to have distinct enzyme se ts having different thermal dependency and to be involved in starch degrada tion to various sugars.