Turnover Rates of Hexokinase I, Phosphofructokinase, Pyruvate Kinase and Creatine Kinase in Slow‐Twitch Soleus Muscle and Heart of the Rabbit

Abstract

Hexokinase I was purified from rabbit heart to a specific activity of 70 U/mg protein. The purified enzyme was electrphoretically homogeneous with an apparent MW of 102,000. Purified immunoglobulins from sheep were used to titrate the percentage of hexokinase I in various tissues of the rabbit. Precipitating antibodies from sheep were also prepared against rabbit muscle MM-creatine kinase, phosphofructokinase [EC 2.7.1.11] and pyruvate kinase [EC 2.7.1.40]. Apparent turnover rates of these phosphotransferases and of hexokinase I [EC 2.7.1.1] were determined in rabbit heart and soleus muscle by immunoprecipitation after single pulse labeling with [U-14Cl]leucine in vivo. Apparent half-lives of phosphofructokinase, pyruvate kinase and hexokinase I were 0.56 day 0.73 day and 0.93 day in rabbit heart. In slow-twitch soleus muscle half-lives of phosphofructokinase, pyruvate kinase, hexokinase I and creatine kinase were 0.63 day, 0.72 day, 0.85 day and 0.82 day. The similarity of the rate constants of degradation of these enzymes is interpreted as an indication that different tissue concentrations result primarily from different rates of synthesis.