SUCCINIC DEHYDROGENASE CONTENT OF INDIVIDUAL MUSCLE FIBERS AT DIFFERENT AGES AND STAGES OF GROWTH

Succinic dehydrogenase was measured cytophotometrically in muscle fibers from mice of different ages. For a short time after birth the concentration of enzyme within the fibers increased. However, the concentration of the enzyme within fibers of mature muscles was entirely dependent on the size of the fiber. Fibers that had undergone further growth had approximately the same total amount but the concentration of enzyme was much decreased because the mitochondrial content of the fiber had apparently been diluted four or five times by additional myofibrillar material. When different anatomical muscles were compared, fibers of the same size were found to have approximately the same enzyme concentration irrespective of what muscle they belonged to. This was so even for the soleus muscle which is a typical mammalian 'red muscle', although in this muscle there were no large fibers and therefore the concentration of succinic dehydrogenase in the muscle as a whole was considerably greater. Measurements on fibers from dystrophic mice revealed that most of the fibers were small and degenerating and had a lower enzyme content than normal. However a few large fibers, particularly the exceptionally large fibers found in the dystrophic biceps brachii, had a greater concentration than normal. © 1969.