Activities of malate dehydrogenase, 3-hydroxyacyl-CoA dehydrogenase and fructose-1,6-diphosphatase with regard to metabolic subpopulations of fast- and slow-twitch fibres in rabbit muscles

Abstract

Activities of malate dehydrogenase (MDH), 3-hydroxyacyl-CoA dehydrogenase (HAD) and fructose-1,6-diphosphatase (FDPase) were determined in single fibres dissected from freeze-dried rabbit psoas and soleus muscles. Slow-twitch fibres as determined by qualitative ATPase reaction represent a rather uniform population with regard to HAD and MDH activities. In these fibres the two enzymes are in constant proportions. FDPase is found at extremely low activities in slow-twitch fibres and because of its relatively high activity in fast-twitch fibres of soleus and psoas muscle it might be used as a marker enzyme. Fast-twitch fibres in psoas muscle represent a heterogeneous population with regard to activities of MDH as well as of HAD. The two enzyme activities are not proportional in fasttwitch psoas fibres. These findings suggest the existence of metabolic sub-populations of fast-twitch fibres having a wide range of aerobic oxidative capacities and having differences in their capacity to oxidizing fatty acids.