No abstract

No abstract

An antibody prepared against purified cytochrome c-553 from Nostoc muscorum inhibits the redox function of cytochrome c-553 as checked by a diaphorase assay. 20 to 30% inhibition of NADPH-driven respiratory and light-induced oxygen uptake by Nostoc thylakoids is observed when cytochrome c-553 specific antibodies were applied. However, only 30 to 50% of the total cytochrome c-553 content is released from isolated membrane material, thus being accessible to antibodies. Supplementing the isolated membrane material with excess Nostoc cytochrome before adding the antibody abolishes inhibition. The data provide further evidence for soluble cytochrome c-553 being a link between photosynthetic and respiratory electron transport in blue- green algae.

No 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.