Induction of ornithine decarboxylase activity in baby-hamster kidney cells.

ment of the rat. 'Malic' enzymes from the livers of normal and hyperthyroid rats were found to be kinetically, electrophoretically and immunologically identical. Hence the increased activity found in hyperthyroid rat liver was due to an increase in the same form of enzyme protein as in normal liver. 'Malic' -enzyme was therefore purified from the livers of hyperthyroid rats by a modification of the method of Hsu & Lardy (1967) for pigeon liver 'malic' enzyme. The final preparation (specific activity 21-23 units/mg ofprotein) washomogeneous as assessed by analytical centrifugation, by electrophoresis (including isoelectric focusing) and by immunological analysis. A specific antiserum to purified 'malic' enzyme was raised in rabbits and the enzyme-anti-enzyme precipitin reaction was subsequently characterized both qualitatively and quantitatively. Dissociation of this antigen-antibody complex with sodium dodecyl sulphate and subsequent electrophoresis yielded three protein components, the subunit of 'malic' enzyme (molecular weight 61000) and the light and the heavy chains of the y-globulin antibody. Administration of L-[4,5-3H]leucine in vivo to rats aged 30-35 days and isolation ofimmunoprecipitable hepatic 'malic' enzyme by the specific antiserum indicated that the relative rate of enzyme synthesis was decreased threefold by starvation for 48h or in alloxan-diabetic animals and was increased almost fourfold on treatment with thyroxine, compared with the rate in the normal animal. Rats aged 30 days and maintained on a solid milk (high-fat) diet from weaning also showed a threefold decrease in the synthesis of this enzyme. The development of hepatic 'malic' enzyme was prematurely evoked in animals throughout the suckling and weaning periods by treatment with thyroxine. Increased synthesis of 'malic' enzyme occurred in both suckling (9 and 15 days old) and weaned (23 days old) animals after treatment with thyroxine. Early weaning (at 16 days) also caused increased synthesis of this enzyme at 23 days of age. Changes in 'malic' enzyme activity in rat liver during adaptation and development can therefore be partially ascribed to a change in the rate of enzyme synthesis [cf. Silpananta & Goodridge (1971) on chick liver].