Purification and characterization of the higher plant enzyme L-canaline reductase.
A newly discovered enzyme, L-canaline reductase (NADPH:L-canaline oxidoreductase, EC 1.6.6-), has been isolated and purified from 10-day-old leaves of the jack bean Canavalia ensiformis (Leguminosae). This higher plant is representative of a large number of legumes that synthesize L-canavanine, an important nitrogen-storing nonprotein amino acid. Canavanine-storing legumes contain arginase, which hydrolyzes L-canavanine to form the toxic metabolite L-canaline. Canaline reductase, having a mass of approximately 167 kDa and composed of 82-kDa dimers, catalyzes a NADPH-dependent reductive cleavage of L-canaline to L-homoserine and ammonia. This is the only enzyme known to use reduced NADP to cleave an O-N bond. Canaline reductase performs at least three important functions for canavanine-synthesizing legumes. First, it detoxifies canaline. Second, it increases by one-half the overall yield of ammoniacal nitrogen released from canavanine. Third, it permits the carbon skeleton of canavanine, a secondary plant metabolite, to support vital primary metabolic reactions.
Rosenthal
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T.H. Morgan School of Biological Sciences, University of Kentucky, Lexington 40506.
D000596:Amino Acids / Q000032:analysis; D002172:Canavanine / Q000378:metabolism; D002845:Chromatography / Q000379:methods; D007887:Fabaceae / Q000201:enzymology*; D007700:Kinetics; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism*; D010946:Plants, Medicinal; D013057:Spectrum Analysis; D013379:Substrate Specificity
D000596:Amino Acids; D002172:Canavanine; D009247:NADH, NADPH Oxidoreductases; C073292:L-canaline reductase