Characterization of three bioenergetically active respiratory terminal oxidases in the cyanobacterium Synechocystis sp strain PCC 6803

Synechocystis sp. PCC 6803 contains three respiratory terminal oxidases (RT Os): cytochrome c oxidase (Cox), quinol oxidase (Cyd), and alternate RTO (A RTO). Mutants lacking combinations of the RTOs were used to characterize th ese key enzymes of respiration. Pentachlorophenol and 2-heptyl-4-hydroxy-qu inoline-N-oxide inhibited Cvd completely, but had little effect on electron transport to the other RTOs, KCN inhibited all three RTOs but the in vivo K-I for Cox and Cyd was quite different (7 vs. 27 muM), as was their affini ty for oxygen (K-M 1.0 vs. 0.35 muM). ARTO has a very low respiratory activ ity. However, when uptake of 3-O-methylglucose, an active H+ co-transport, was used to monitor energization of the cytoplasmic membrane, ARTO was simi larly effective as the other RTOs. As removal of the gene for cytochrome C- 553 had the same effects as removal of ARTO genes, we propose that the ARTO might be a second Cox. The possible functions, localization and regulation of the RTOs are discussed, (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.