Regulation of respiration and energy transduction in cytochrome c oxidase isozymes by allosteric effectors.
The binding of TNP-ATP (2' or 3'-O-(2,4,6-trinitrophenyl)-ATP) to cytochrome c oxidase (COX) from bovine heart and liver and to the two-subunit COX of Paracoccus denitrificans was measured by its change of fluorescence. Three binding sites, two with high (dissociation constant Kd = 0.2 microM) and one with lower affinity (Kd = 0.9 microM), were found at COX from bovine heart and liver, while the Paracoccus enzyme showed only one binding site (Kd = 3.6 microM). The binding of [35S]ATP alpha S was measured by equilibrium dialysis and revealed seven binding sites at the heart enzyme (Kd = 7.5 microM) and six at the liver enzyme (Kd = 12 microM). The Paracoccus enzyme had only one binding site (Kd = 16 microM). The effect of variable intraliposomal ATP/ADP ratios, but at constant total concentration of [ATP + ADP] = 5 mM, on the H+/e- stoichiometry of reconstituted COX from bovine heart and liver were studied. Above 98% ATP the H+/e- stoichiometry of the heart enzyme decreased to about half of the value measured at 100% ATP. In contrast, the H+/e-stoichiometry of the liver enzyme was not influenced by the ATP/ADP ratio. It is suggested that high intramitochondrial ATP/ADP ratios, corresponding to low cellular work load, will decrease the efficiency of energy transduction and result in elevated thermogenesis for the maintenance of body temperature.
Kadenbach
B
B
Philipps-Universität, Marburg, Germany.
Frank
V
V
Rieger
T
T
Napiwotzki
J
J
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000378:metabolism*; D005453:Fluorescence; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D010231:Paracoccus denitrificans / Q000201:enzymology*
D007527:Isoenzymes; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV