Israel Zelitch

Samuel W. Johnson Distinguished Scientist, The Connecticut Agricultural Experiment Station. Research focuses on the regulation of photorespiration, a process that lowers net photosynthesis in C(3) plants. In the course of these studies he unravelled the enzymatic mechanism of the glycolate oxidase reaction and showed the importance of hydrogen peroxide as a byproduct. He discovered enzymes catalyzing the reduction of glyoxylate and hydroxypyruvate, and found (alpha)-hydroxysulfonates were competitive inhibitors of glycolate oxidase. He added these inhibitors to leaves and showed that glycolate metabolism was an essential part of photorespiration, and: (1) glycolate was synthesized only in light as an early product of photosynthetic CO(2) assimilation, (2) the rate of glycolate oxidation consumed a sizable fraction of net photosynthesis in C(3) but not C(4) plants, and (3) that glycolate metabolism increased greatly at higher temperatures. Recently he has shown that when photorespiration rates are high, as at higher temperatures, genetically increasing leaf catalase activity reduces photorespiration and increases net photosynthetic CO(2) assimilation.