Body Weight, Activities of Cytochrome Oxidase and Electron Transport System in the Liver of the American Plaice Hippoglossoides platessoides. Can these Activities Serve as Indicators of Metabolism?

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Abstract
In many organisms including fish, metabolic rate (O2 consumption rate, .ovrhdot.VO2) is related to body weight (W) allometrically, i.e., by a function of the form .ovrhdot.VO2 = aWb, b often taking a value near 0.8. Metabolic oxidation is controlled by a chain of enzymes and cytochromes known as respiratory electron transport system. The hypothesis that the activities of the hepatic electron transport system (ETS) and its terminal oxidase (cytochrome oxidase, CYTOX) are related to W by a similar function, was investigated for a natural population of American plaice H. platessoides. All measures of hepatic ETS and CYTOX activities (Ki) turned out to be significantly related to W by a function of the form Ki = cWd, where d = rate of change of enzyme activities with W. The values of d for the total hepatic ETS and CYTOX activities were 0.90 .+-. 0.03 (SE) and 0.83 .+-. 0.04 (SE), respectively. These values were close to 0.8, the value of the exponent for the .ovrhdot.VO2-W relationship in H. platessoides. The possibility that CYTOX and ETS activities might serve as indicators of routine metabolic rate is discussed in relation to a set of criteria proposed.