Abstract
Filaments of N2-grown Anabaena variabilis exhibit soluble NADPH- and membrane-bound NADH-oxidizing activities. The NADPH-specific enzyme has been identified as ferredoxin-NADP oxidoreductase (FNR; EC 1.18.1.2) by the thionicotinamide-NADP transhydrogenase test, a ferredoxin-dependent hydrogenase assay, and by diaphorase systems. The FNR is easily removed by washing of French-press-prepared membranes. Concurrently, a loss of NADPH-dependent respiration is apparent, which is not reconstitutable by addition of Anabaena cytochrome c-553. The NADH-oxidizing activity, however, is only slightly affected by the washing procedure, and is completely reconstituted by cytochrome c-553. NADPH-dependent oxygen uptake is strongly inhibited by NADP, whereas inhibition of NADH-dependent oxygen uptake by NAD is less pronounced. The data give evidence that NADH and NADPH oxidations linked to the respiratory chain are mediated by two different enzymes.
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