Effects of chronic alcohol consumption on the steady-state kinetics properties of cytochrome oxidase in rat liver.
The effect of chronic alcohol consumption on steady-state kinetic characteristics of cytochrome oxidase in rat liver was studied using submitochondrial particles prepared from ethanol-fed and control rats. Preparations from both control and alcoholic rats had equivalent apparent Km values for cytochrome c of 13 microM in the presence of phenazine methosulfate or 19 microM with N,N,N',N'-tetramethylphenylene diamine as oxidation-reduction mediators at physiological ionic strength. Both preparations showed comparable stimulation (approx. 3-fold) of oxidase activity following detergent solubilization of the membrane and similar temperature dependence for oxidase activity. Under all conditions, preparations from alcohol-fed rats displayed 30 to 50% lower rats of cytochrome oxidase activity per unit membrane protein than those from control rats. The diminution in specific activity per mg protein was accompanied by a similar decline in heme aa3 content, as has been noted in previous studies. When expressed on a turnover number basis, the molecular activity of cytochrome oxidase (natoms O/min per nmol heme a) was equivalent in both alcoholic and control preparations. The results indicate that the intrinsic kinetic characteristics of cytochrome oxidase are not changed by alcohol consumption. The data suggest that the characteristic decline in heme aa3 content and cytochrome oxidase specific activity seen in ethanol-fed rats does not arise from alterations in the accessibility of the oxidase towards cytochrome c, or from changes in bulk phase lipid composition or physical properties. The results support the conclusion that ethanol consumption decreases the membrane content of functionally active oxidase molecules, but does not change the catalytic properties of these oxidase molecules.
Thayer
W S
WS
Department of Pathology, Hahnemann University, School of Medicine, Philadelphia, PA 19102.
Cummings
J J
JJ
D000437:Alcoholism / Q000201:enzymology*; D000818:Animals; D002463:Cell Membrane Permeability; D003574:Cytochrome c Group / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008773:Methylphenazonium Methosulfate / Q000494:pharmacology; D008930:Mitochondria, Liver / Q000201:enzymology*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D051381:Rats; D011919:Rats, Inbred Strains; D013367:Submitochondrial Particles / Q000201:enzymology; D013696:Temperature; D013772:Tetramethylphenylenediamine / Q000494:pharmacology
D003574:Cytochrome c Group; C027728:heme a; D008773:Methylphenazonium Methosulfate; D006418:Heme; D003576:Electron Transport Complex IV; D013772:Tetramethylphenylenediamine