Allosteric properties of cyanobacterial cytochrome c oxidase: Inhibition of the coupled enzyme by ATP and stimulation by ADP

Thorough analysis of the cta operon of Synechocystis sp. PCC6803 (grown in high-concentration salt medium to enhance the expression of respiratory pro teins) showed that, apart from ctaCDE and Fb genes potentially encoding sub units I, II, III, and a small pseudo-bacteria-like subunit-IV of unknown fu nction, a large mitochondria-like cta-Fm gene and a pronounced terminator s tructure are additional components of the operon, The deduced cta Fm gene p roduct shows similar to 50% and 20% sequence identity to the Saccharomyces cerevisiae and beef heart mitochondrial COIV proteins, respectively, It als o shows amino acid regions (near the N terminus, on the cytosolic side) wit h conspicuous sequence similarities to adenylate-binding proteins such as A TP synthase beta subunit Walker A and B consensus regions or to adenylate k inase, We suggest that, similar to the situation with beef heart mitochondr ia, it is the mitochondria-like subunit-IV of the cyanobacterial aa3-type c ytochrome-e oxidase that confers allosteric properties to the cyanobacteria l enzyme, the H+/e(-) ratios of cytochrome c oxidation being significantly lowered by ATP (intravesicular or intraliposomal) but enhanced by ADP. Ther efore, the antagonistic action of ATP and ADP was in a way that the redox r eaction proper, was always significantly less affected than the coupled pro ton translocation. Evolutionary and ecological implications of the unusual allosteric regulation of a prokaryotic cytochrome-e oxidase is discussed.