The ratio of 3‐hydroxyacyl‐CoA dehydrogenase to lipoamide dehydrogenase activity in individual muscle fibers: Mitochondrial specialization for source of energy

Abstract

3-Hydroxyacyl-CoA dehydrogenase (HAD) has been widely used to assess the capacity for fatty acid oxidation by different muscle fiber types, with various Krebs cycle enzymes as a base for comparison. We have measured this enzyme in individual lyophilized fibers of the guinea pig soleus and the white and red portions of the vastus lateralis, and compared its activity in each fiber with that of lipoamide dehydrogenase (LAD), which as a part of the pyruvate dehydrogenase complex fulfills a function similar to HAD in forming acetyl-CoA, but from pyruvate and, thus, mainly from a carbohydrate source. The mean HAD/LAD ratio was 17.2 +/- 3 in the red vastus, 24.9 +/- 3 in the white vastus, and 43.7 +/- 10 in the soleus, all differences being highly significant. The two types of fast fibers were not distinguished from one another by the enzyme ratio within either the white or the red portion of the vastus lateralis. Data from all of the fast fibers taken together indicate a close correlation (0.93) between the two enzymes, whereas values from the soleus indicate a specialization of the mitochondria of the slow muscle fibers for the oxidation of fatty acids.

The impact of biochemical methods for single muscle fibre analysis

“…However, fast and slow fibre populations can be separated using specific enzyme activity ratios: e.g. adenylate kinase to lactate dehydrogenase, 3‐hydroxyacyl‐CoA dehydrogenase to lipoamide dehydrogenase, malate dehydrogenase to lactate dehydrogenase, hexokinase to phosphofructokinase, hexokinase to fructosebisphosphatase, and 3‐hydroxyacyl‐CoA dehydrogenase to phosphofructokinase ratios (Hirsch et al . 1982, Hintz et al .…”