CYANIDE-INSENSITIVE OXYGEN-UPTAKE AND PYRIDINE-NUCLEOTIDE DEHYDROGENASES IN THE CYANOBACTERIUM ANABAENA PCC-7120

The nature and subcellular location of cyanide-insensitive respiration and the pyridine nucleotide dehydrogenases were investigated in the cyanobacterium Anabaena PCC 7120. Oxygen uptake by isolated thylakoid membranes in the presence of either NADH, NADPH or duroquinol as substrates, was partially insensitive to KCN at concentrations which completely inhibited plasma membrane-mediated oxygen uptake. The cyanide-insensitive oxidase was not inhibited by salicyl hydroxamic acid (SHAM) or by n-propyl gallate (n-PG), which are inhibitors of the plant mitochondrial alternative oxidase; nor did total membrane proteins cross-react with antibodies raised against the alternative oxidase. We conclude that cyanide-insensitive oxidation is confined to the thylakoid membrane in Anabaena PCC 7120 and is not catalysed by the alternative oxidase responsible for cyanide-insensitive respiration in plants. Both plasma membranes and thylakoid membranes oxidised NADH and NADPH. Isolated plasma membrane was shown to contain a single type-1 dehydrogenase that is antigenically homologous to complex I of mitochondria and sensitive to the respiratory poison rotenone, but which oxidises both NADH and NADPH. The thylakoid membrane was shown to contain two NAD(P)H dehydrogenases: that responsible for NADH oxidation has inhibition characteristics of a type-2 dehydrogenase while NADPH oxidation may be catalysed by ferredoxin NADP+-oxidoreductase, the last enzyme in the photosynthetic electron transport chain.