An inverse relation between mitochondrial hexokinase content and phosphoglucomutase activity of rat tissues.

The hexokinase: fumarase ratios of mitochondria isolated from ten tissues of the rat were determined, and compared with the tissue content of phosphoglucomutase and phosphorylase, taken as representatives of enzymes concerned with glycogen metabolism. A generally inverse relationship was found between the mitochondrial hexokinase: fumarase ratio and phosphoglucomutase levels. The cytochrome: fumarase ratios were relatively invariant in these same mitochondria. The results are interpreted as indicating a specialization of mitochondria, with increased amounts to hexokinase being associated with the mitochondria in tissues exhibiting less dependence on glycogen metabolism, as judged from phosphoglucomutase levels.