Myoglobin content and the activities of enzymes of energy metabolism in red and white fish hearts

Summary The myoglobin content of representative red and white coloured fish hearts was quantitated. It was confirmed that the macroscopic difference in appcarance is due to the presence or absence of myoglobin. Thereafter, the cytochrome c content as well as the maximal activities of key enzymes of energy metabolism were assessed in myoglobin-rich sea raven (Hemitripterus americanus) and myoglobin-poor ocean pout (Macrozoarces americanus) hearts. Both species are sluggish benthic dwellers that occur in similar habitats in the North Atlantic Ocean. The activities of enzymes associated with aerobic metabolism were similar in sea raven and ocean pout hearts, but far in excess of activities observed from white skeletal muscle. The two hearts also displayed comparable activities of enzymes associated with anaerobic energy metabolism. It therefore appears that the capacity to produce reducing equivalents for the electron transport system is similar in two selected fish hearts despite great differences in myoglobin content.