Biosynthesis of rat liver pyruvate kinase

Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of immunoprecipitates of liver cytosol with anti-(L-type pyruvate kinase) serum revealed proteins of mol.wt. 56000 and 42000 in addition to the heavy and light chains. The ratio of the 56000mol.wt. to the 42000mol.wt. protein increased under dietary conditions that resulted in an increase in the apparent specific activity of hepatic pyruvate kinase. The 42000mol.wt. protein was removed from immunoprecipitates if the liver cytosol was partially purified by pH precipitation and (NH4)2SO4 fractionation before addition of the antiserum. This technique may be used to analyse the formation of pure L-type pyruvate kinase in liver. By using H14CO3labelling, the ti of L-type pyruvate kinase was estimated as 75 ± 1.7 h in post-weaned high-carbohydrate-diet-fed rats. Before weaning there was little immunoreactive pyruvate kinase in rat liver cytosol. Induction began between 6 and 24h after weaning and reached a maximum value 120h after weaning. When clearly enhanced total pyruvate kinase activity was first observed at 24 h post-weaning, the apparent specific activity of hepatic pyruvate kinase was considerably lower than the specific activity of the pure isolated enzyme. When the induction of L-type pyruvate kinase was monitored by the incorporation of L-[4,5-3H]leucine, the maximum rate of synthesis occurred 24-48 h after weaning. After this period synthesis declined, indicating a relatively slow turnover of the enzyme once the enzyme concentration was established in the liver.