Decreased cytochrome oxidase activity in hepatic mitochondria after chronic ethanol consumption and the possible role of decreased cytochrome aa3 content and changes in phospholipids

In ethanol-fed baboons, hepatic mitochondrial cytochrome oxidase activity and cytochrome aa₃ content were significantly decreased by 58.3 and 50.5%, respectively, compared to their pair-fed controls. However, there was no significant correlation between the two, suggesting that other factors in addition to cytochrome aa₃ may be responsible for the depression in cytochrome oxidase activity. The total phospholipid content of the mitochondrial membranes was significantly decreased (0.24 ± 0.03 μmol of phospholipid phosphorus/mg of protein vs. 0.32 ± 0.04 in controls). This change was accounted for, in part, by the significant decrease in the levels of phosphatidylcholine and cardiolipin. In addition, the fatty acid pattern of the phospholipids was changed. There was a marked increase in the relative amounts of oleic and linoleic acid and a decrease in arachidonic acid. These changes were associated with an increase in the activity of phospholipase A₂. The reactivation rate of phospholipid-depleted cytochrome oxidase by endogenous phospholipids from ethanol-fed baboons was significantly lower than that by phospholipid from pair-fed controls, when measured at an optimal phospholipid to protein ratio. Thus, it appears that alterations in the phospholipid composition of the mitochondrial membranes are responsible, at least in part, for the depression of cytochrome oxidase activity produced by chronic ethanol consumption.