Biochemical Correlates of Energy-Metabolism in Muscles Used to Power Hopping by Kangaroos

Abstract

Energy metabolism in the ankle extensor muscles used to power kangaroo hopping was investigated by examining myoglobin content, pH buffering capacity, distribution and properties of LDH isozymes, maximum activities of enzymes, fibre types and muscle weights. The large gastrocnemius and plantaris muscles contain predominantly IIA and IIB fibres, and display considerable potential for both aerobic and anaerobic ATP production during locomotion. In the small soleus muscle, the presence of only Type I fibres, lower pH buffering capacity, higher proportions of LDH H subunits and low enzyme activities imply a predominantly aerobic metabolism with limited potential for ATP production. Interspecific comparisons showed differences in the relative dependence on aerobic and anaerobic ATP production that correlate with locomotory behaviour. The major ankle extensor muscles of macropods may differ from equivalent muscles of eutherians in an apparent high capacity for aerobic glycolysis relative to the use of fatty acids as an aerobic fuel.