Protein degradation in rat liver during post-natal development

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Abstract
Protein degradation rates for liver subcellular and submitochondrial fractions from neonatal (8 day), weanling (25 day) and adult rats were estimated by the double-isotope method with NaH14CO3 and [3H]arginine as the radiolabeled precursors. Decreased protein degradation rates were found during post-natal development for homogenate, nuclear, mitochondrial, lysosomal and microsomal proteins. A decrease in degradation rates for the immunoisolated subunits of monoamine oxidase and pyruvate dehydrogenase was also observed in neonatal and weanling rats, respectively. Coordinate degradation of the subunits of the multi-subunit enzyme pyruvate dehydrogenase is suggested. Pyruvate dehydrogenase has a faster rate of degradation in adult rat liver than does cytochrome oxidase. There is apparent heterogeneity of protein degradation rates in the mitochondrial outer membrane and intermembrane space fractions at each developmental stage but not in the mitochondrial inner membrane or matrix fractions. Results obtained for protein degradation rates in adult rat liver by the method of Burgess, Walker and Mayer in general confirmed the results obtained for the adult rat liver by the above method. No evidence of a subunit-size relationship for protein degradation was found for proteins in any subcellular or submitochondrial fraction.