Purification and Characterization of Polygalacturonase from Polished Rice

概要

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Two isoforms of polygalacturonase (PG, E. C. 3. 2. 1.15), namely, PG-1 and PG-2, were purified from the endosperm of polished rice, (<I>Oryza sativa</I> cv. Koshihikari, the most extensively producted rice variety in Japan). PBE 94 chromatforcusing indicated <I>p</I>Is of 5.6 and 5.1 for PG-1 and PG-2, respectively. These enzymes had same molecular weights approx. 67 kDa and consisted of a monomer. PG-1 and PG-2 exhibited optimum activities at pHs 5.0 and 4.5, respectively, and optimum temperatures of 60°C. Furthermore, these were stable at near-neutral pHs and retained 40% of their activities at 70°C. These results suggest that PG-1 and PG-2 are activated when rice is being cooked, and that the amount of pectin that combined with cells decreased by approximately 40%. Moreover, purified polygalacturonases decomposed pectin during rice cooking. It is surmised that the two PGs in the rice endosperms, decompose the pectin during rice cooking, thereby loosening the intercellular cement that gives firmness to plant tissues, and affecting the texture of cooked rice.
日本食品保蔵科学会の論文