Soluble electron-transport activities in fresh and aged turnip tissue

Summary A soluble (supernatant) fraction from turnips catalyses the reduction of both FeCN and DCPIP but usually not cytochrome c in the presence of either NADH or NADPH. Slicing and aging turnip tissue induces an increase in these activities as well as the development of an NADH-cytochrome c reductase activity.(NH₄)₂SO₄ and Sephadex fractionation indicated that at least three enzymes were involved: an NADH-cytochrome-c reductase, an NADH-FeCN reductase, and an NAD(P)H-DCPIP and FeCN reductase. While the latter reductase had an acid pH optimum, indicating vacuolar origin, the NADH-cytochrome-c and FeCN reductases both had neutral pH optima, indicating cytoplasmic origin. Characterization of the NADH-specific reductases indicated that NADH-FeCN reductase may be a soluble form of the microsomal membrane NADH dehydrogenase but that NADH-cytochrome-c reductase may be normally soluble and possibly involved in cyanide-sensitive NADH oxidation.The induced development of all three reductases was inhibited by 6-methylpurine, ethionine and cycloheximide, indicating dependence on both RNA and protein synthesis. The inhibition by cycloheximide could be reversed but this reversion required a 20-h washing-out period to be complete.Abbreviations DCPIP 2,6-dichlorophenol indophenol - FeCN ferricyanide - NO QNO 2-n-nonylhydroxyquinoline-N-oxide - pCMB p-chloromercuribenzoate - SF soluble fraction