Differential hormonal regulation of L-glycerol 3-phosphate dehydrogenase in rat brain and skeletal muscle.

The level of l-glycerol 3-phosphate dehydrogenase (EC 1.1.1.8) is regulated in the rat brain by glucocorticoids. Following hypophysectomy, the concentration of brain glycerol-3-P dehydrogenase decreases to about 40% of the control. By immunotitration, we have demonstrated that this decrease in glycerol-3-P dehydrogenase activity is due to fewer enzyme molecules rather than less efficient ones. We also demonstrated that the enzyme remaining in the brain after hypophysectomy is identical to that found in the brains of control littermates, as determined by gel permeation chromatography, pH optimum, heat lability, electrophoretic mobility, and Ouchterlony double-diffusion analysis. Since the concentration of glycerol-3-P dehydrogenase in skeletal muscle is not regulated by glucocorticoids, we also compared the brain enzyme to the muscle enzyme. By the above criteria, skeletal muscle glycerol phosphate dehydrogenase is identical to the brain enzyme. This suggests that the same structural gene codes for glycerol-3-P dehydrogenase in brain and muscle and that the difference in response to glucocorticoids is due to the presence of a specific regulatory mechanism in brain that is absent in muscle.