Role of ATP in the regulation of branched-chain alpha-keto acid dehydrogenase activity in liver and muscle mitochondria of fed, fasted, and diabetic rats.

H S Paul,S A Adibi

doi:10.1016/s0021-9258(18)34607-6

Abstract

The activity of branched-chain alpha-keto acid (BCKA) dehydrogenase was increased after preincubation of liver and muscle mitochondria of control rats. Preincubation depleted mitochondrial ATP. Addition of ATP prevented the activation of BCKA dehydrogenase as well as reversed the activity of a fully activated enzyme to normal. Inhibition of phosphatase blocked the activation of BCKA dehydrogenase. There was a small or no increase in BCKA dehydrogenase activity when mitochondria from tissues of fasted, diabetic, and clofibrate-treated rats were preincubated. In fasted and diabetic rats, ATP was either less effective or failed to reverse the increased dehydrogenase activity in preincubated mitochondria. The concentration of ATP in liver and muscle mitochondria of diabetic rats was approximately one-half that of the control rats. We conclude that (a) in the fed state approximately 30-40% of BCKA dehydrogenase exists in the active form. The enzyme can be fully activated by preincubation of mitochondria which causes the depletion of ATP. Phosphatase is necessary for this activation. (b) In fasted, diabetic, and clofibrate-treated rats, approximately 70-100% of the enzyme exists in the active form which may be related to the mitochondrial depletion of ATP in vivo, and (c) while ATP can reverse the activation in control rats, it fails to do so in diabetic rats suggesting that other metabolic alterations may be involved in the regulation of BCKA dehydrogenase in diabetes.

Highlights

We conclude that (a)in the fed state approximately 30-40% of branched-chain a-keto acid (BCKA) dehydrogenase exists in the active form
(6) In fasted, diabetic, and clofibrate-treated rats, approximately 70-100% of the enzymeexists in theactive form which may berelated to the mitochondrial depletion of ATP in vivo, and (c) while ATP can reverse theactivation in control rats, it fails to do so in diabetic rats suggesting that other metabolic alterations may be involved in theregulation of BCKA dehydrogenase in diabetes
To test thepossibility that starvation and diabetes might enhance the activity of this enzyme by increased conversion to the active form, we examined the effect of preincubation of mitochondria from tissues of fasted and diabetic rats

Summary

Activation of BCKA Dehydrogenase

BCKA dehydrogenase activities in freshly prepared liver and skeletal muscle mitochondria of control rats were approximately and 7 nmol/mg of proteid 30 min, respectively (Fig. 1). A number of possibilities could account for the increased activity of BCKA dehydrogenase with preincubation These include (a)an alteration in the mitochondrial redox state, ( h ) disruption of mitochondria, ( c ) depletion of mitochondrial ATP, and (d)alteration in the activity of a putative phosphoprotein phosphatase. To furtherexplore this possibility, we preincubated liver (60min) and muscle (30min) mitochondria with and without ATP and ATP-regenerating system. Addition of ATP completely reversed the increased dehydrogenase activity brought about by preincubation of liver and muscle mitochondria. Without preincubation both liver and muscle mitochondria contain basal activity of BCKA dehydrogenase. These effects of NaF and pyrophosphate suggest that phosphatase is necessary for the activation of BCKA dehydrogenase by preincubation of mitochondria

Activation of Dehydrogenase inPerturbed Metabolic Conditions

DISCUSSION

MATERIAL TO