Submitted to: Southern Association of Agricultural Scientists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/30/2003
Publication Date: 1/16/2004
Citation: Qin, Z., Counce, P.A., Bryant, R.J., Thompson, V.A., Moldenhauer, K.A. 2004. Isolation of multiple isoforms of endosperm sucrose synthase from Guichao Oryza sativa. Southern Association of Agricultural Scientists Bulletin: Biochemistry and Biotechnology. 17:35-42. Interpretive Summary: Sucrose synthase activity in rice potentially limits rice crop yields, thus, profit. In order to better understand the enzyme better, we isolated the enzyme from a rice cultivar, Guichao. The study of the activity of this important enzyme will give scientists a better understanding of the conditions under which it will function best.
Technical Abstract: Sucrose synthase activity in rice potentially limits rice crop yields. This is because the carbon that forms starch enters the developing rice grain as sucrose and that sucrose must be broken down by the enzyme sucrose synthase to form the precursors of starch, UDP glucose and fructose. By a series of steps, these materials are converted into ADP glucose that is incorporated into starch chains by the action of starch synthase. Earlier research efforts indicated that endosperm sucrose synthase activity during grain filling was higher in Guichao rice than in U.S. rice cultivars. We set about to purify sucrose synthase from Guichao endosperm as part of an overall research effort to understand the physiological reasons for the high yields of Guichao compared to U.S. rice cultivars. The purification protocol utilized ion exchange chromatography, hydrophobic interaction chromatography and a Resource Q column. Incorporation of hydrophobic interaction into the protocol came about as a result of preliminary experiments with ammonium sulfate precipitation of the enzyme. One important finding was that hydrophobic interaction is valuable in the isolation of sucrose synthase from rice endosperm. The enzyme was purified 10.3 folds and had a specific activity of 33.7 U/mg protein. Four bands of the protein were identified with a Native-PAGE, four activity peaks from the Resource Q column were found but eight separate protein bands were identified using isoelectric focusing. Although more work is needed, considerable progress toward purified sucrose synthase from Guichao rice has been made.