Simulation of the Physiological Role of Spinach Glyoxylate Reductase (NADP^+) in Chloroplasts

概要

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1. NADPH-Glyoxylate reductase was separated from hydroxypyruvate reductase and characterized at pH 7.2 and 8.0. The enzyme can work at pH 8.0; the Km value for glyoxylate at this pH was 0.38 mM, and the Vmax there was about 40% of that at pH 7.2. The enzyme can use both NADPH and NADH as the cofactors, and the ratio of its activities depending on these cofactors was 4.4:1. 2. The specific activity of the enzyme in isolated chloroplasts was 20 μmole・mg^<-1>Chl・h^<-1>, and that in the crude extract was 200 μmole・mg^<-1>Chl・h^<-1>. The discrepancy was ascribed to the leakage of the enzyme from the isolated chloroplasts and the difficulty in estimation of the enzyme activity in the crude extract because of contamination by hydroxypyruvate reductase and lactate dehydrogenase. 3. The physiological role of the enzyme was simulated in terms of the consumption of reducing equivalents and the scavenging of glyoxylate in the chloroplasts, which inhibits rubisco. According to the simulation the enzyme worked as a scavenger when the conductance of the chloroplast membrane against glyoxylate was less than 5×10^<-5>cm・sec^<-1>; otherwise it worked as a member of the shuttle of consumption of the reducing equivalents in the chloroplast.
大阪府立大学の論文
1990-03-31