Adrenergic regulation of Rana balcanica erythrocyte pyruvate kinase

Abstract

The regulation of pyruvate kinase activity by noradrenaline was investigated in Rana balcanica red cells. Thirty minutes of noradrenaline incubation induced a significant increase in the V _o/V _max ratio of pyruvate kinase. The S _0.5 for phosphoenolpyruvate of the enzyme significantly increased in the presence of noradrenaline while the K _m for ADP decreased. In response to hormonal stimulation the Na⁺/H⁺ exchange was activated as was shown by the increase in Na⁺ and cyclic adenosine monophosphate from the 3rd min of incubation. All these effects were specific to α₁ and β antagonists. High concentrations of fructose diphosphate significantly activated the enzyme in the presence of noradrenaline but not in its absence. Furthermore, the presence of noradrenaline partially released the inhibition of the enzyme by adenosine triphosphate, inorganic phosphate and 2,3-diphosphoglycerate. The results suggest that noradrenaline stimulates glycolysis through pyruvate kinase activation. The mechanism of stimulation may is through Na⁺/H⁺ exchange activation, cyclic adenosine monophosphate concentration and Na⁺-K⁺-ATPase activation.