Kleczkowski LA, Randall DD, Edwards GE
Oxalate as a Potent and Selective Inhibitor of Spinach (Spinacia-Oleracea) Leaf Nadph-Dependent Hydroxypyruvate Reductase
Biochemical Journal: 1991 276:125-127
Purified spinach (Spinacia oleracea) NADPH-preferring hydroxypyruvate reductase (HPR-2) was potently and selectively inhibited by oxalate, an end product of metabolism in plants. Both hydroxypyruvate- and glyoxylate-dependent rates of the HPR-2 enzyme were affected. Oxalate acted as an uncompetitive inhibitor of the enzyme, with K(i) values of 7 and 36-mu-M for the NADPH/hydroxypyruvate and NADPH/glyoxylate pairs of reactants respectively. Oxalate, at millimolar levels, caused less than 10% inhibition of purified spinach NADH-preferring HPR (HPR-1) and had no effect on purified spinach NADPH-preferring glyoxylate-specific reductase (GR-1). The inhibition of spinach HPR-2 by oxalate is by far the strongest for any known inhibitor of leaf HPR and GR activities. In photosynthetic tissues, oxalate could potentially act as a primary regulator of extraperoxisomal metabolism of hydroxypyruvate and glyoxylate.
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