Distribution and Characterization of Enzymes Causing Starch Degradation in Rice (Oryza sativa Cv. Koshihikari)

Abstract

The thermal dependency and stability of enzymes producing reducing sugar (RS) 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 extracts revealed two peaks of RS-producing activity with different optimum temperatures (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 components of the RS-producing activities with high and low optimum temperatures, respectively. The peak with a high optimum temperature was a more abundant component in the inner endosperm, compared with other parts of the rice grain. Thus, different parts of rice were found to have distinct enzyme sets having different thermal dependency and to be involved in starch degradation to various sugars.

Search for Cell-Wall-Degrading Enzymes of World-Wide Rice Grains by PCR and Their Effects on the Palatability of Rice

“…14) Iwata has reported that the -glucosidase activity showed a positive correlation with the GBSS activity and amylose content. 15) This can be explained by a relationship between -glucosidase and starch accumulation in developing rice.…”

“…14,15) The -glucosidase genes have been identified by Nakai et al during the ripening and germinating stages in rice. 18) We designed primers a (5 0 -ggt aca acg tcg cgt cgg-3 0 , sense) by using from number 128 nucleotide to number 146 nucleotide, and primer b (5 0 -gcc gcc gcc gga gcg cac-3 0 , antisense) by using from number 687 nucleotide to number 705 nucleotide of identified -glucosidase reported by Nakai et al (Fig.…”

Different Distributions of .ALPHA.-Glucosidases and Amylases in Milling Fractions of Rice Grains

“…Nakai et al also demonstrated that ONG2-II is the major isoform in dormant rice and is a post-translational isoform of ONG2-I. The existence of an ONG2-II-like α-glucosidase is implicated in Koshihikari (Awazuhara et al, 2000;Mabashi et al, 2009) and Yamadanishiki (Iwata et al, 2003). the mixtures for 15 h at 4℃.…”

“…The transferred membrane was incubated in 20 mM Tris buffered saline (TBS, pH 7.5) containing 0.1% Tween-20 and 5% skim milk for blocking. The transferred membrane was reEnzyme assays in the dormant rice revealed the distribution of enzyme activity: α-glucosidases in the inner endosperm, α-amylases in the outer layers, and β-amylases in whole grains (Awazuhara et al, 2000;Iwata et al, 2002). However, the particular distribution of each enzyme isoform in dormant grains is unclear.…”

Distribution of Starch-degrading Enzymes in Rice Grains of Different Cultivars and Elution Behavior during Cooking

“…Nakai et al also demonstrated that ONG2-II is the major isoform in dormant rice and is a post-translational isoform of ONG2-I. The existence of an ONG2-II-like α-glucosidase is implicated in Koshihikari (Awazuhara et al, 2000;Mabashi et al, 2009) and Yamadanishiki (Iwata et al, 2003). Isoamylases and pullulanase are enzymes that hydrolyze the α-1,6-glucosidic linkage of amylopectin.…”