Effects of hydroxylamine and molybdate on the formation of nitrate reductase in the yeast Rhodotorula

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NADPH-nitrate reductase (NR) and NADPH-cytochrome c reductase (CR) activities of Rhodotorula glutinis var. salinaria cells grown in nitrate medium supplied with hydroxylamine (0.2 mM) were respectively 1.6- and 3.1-fold higher than those of cells grown without hydroxylamine. NR formed in nitrate plus hydroxylamine medium is almost totally in an inactive form which is reactivated in vitro by K_3Fe(CN)_6. When molybdate (10^<-7> M) was supplied to this medium, total (active plus inactive) NR activity increased further about twofold but CR activity somewhat decreased. In ordinary nitrate medium, such molybdate effects were small. Most of the CR derepressed (induced) excessively in the nitrate plus hydroxylamine medium had a molecular size similar to NR on the basis of Bio-Gel A 1.5 m chromatography. Some other properties of CR formed in this medium were the same as those of the CR moiety of NR. Adding molybdate to the nitrate plus hydroxylamine medium after growing the cells for 20 hr induced the development of NR activity without any increase in CR activity. This induction was completely blocked by cycloheximide, puromycin and L-canavanine but not completely by 6-methylpurine. Ammonium repressed this induction with markedly decreasing CR activity. The roles of hydroxylamine and molybdate in the formation of NR are discussed.
日本植物生理学会の論文