Kleczkowski LA, Edwards GE, Randall DD
Effects of oxalate on the reduction of hydroxypyruvate and glyoxylate in leaves.
Phytochemistry: 1992 31:51-54
Oxalate was found to be a
potent uncompetitive, or mixed, inhibitor of the partially purified
NADPH-preferring hydroxypyruvate reductase (HPR-2) from a mutant of
barley which lacks the NADH-preferring HPR (HPR-1). Both
hydroxypyruvate and glyoxylate-dependent rates of the HPR-2 enzyme were
inhibited by oxalate, with the experimentally determined K(i) values of
3-5-mu-M, depending on variable substrate. Oxalate did not affect the
activity of barley NADPH-preferring glyoxylate-specific reductase
(GR-1), and had only a negligible effect on HPR-1 from wild-type
barley. The selective effect of oxalate, as seen for barley HPR-2, was
confirmed in studies on partially purified reductases from leaves of
maize, pea, soybean and spinach. In all cases, oxalate acted
independently from acetohydroxamate, a selective inhibitor of GR-1.
Inhibition by oxalate provides an accurate measure of the contribution
of HPR-2 to the overall activities of reductases in leaf extracts and
partially purified preparations.
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