ABSTRACT
Ascorbic acid is believed to protect cells from oxidative damage by reacting with oxygen-derived free radicals. We investigated whether ascorbic acid would affect the rate of breakdown of skeletal muscle proteins in extracts exposed to hydrogen peroxide. Ascorbic acid (20 mmol/L) alone had little or no effect on the rate of ATP-independent or ATP-dependent breakdown of proteins in chicken skeletal muscle. Pretreatment of chicken skeletal muscle extracts with 10 mmol/L H2O2 resulted in a complete loss of ATP-dependent proteolysis and a significant increase (14- to 15-fold) in the rate of ATP-independent protein breakdown. Ascorbic acid (20 mmol/L) did not prevent H2O2 (10 mmol/L) from inactivating the ATP-dependent proteolytic pathway in skeletal muscle. However, ascorbic acid (20 mmol/L) prevented the H2O2-induced increase in the ATP-independent proteolysis of endogenous muscle proteins. Ascorbic acid also slowed the rate of hydrolysis of exogenously added [3H]superoxide dismutase exposed to H2O2 and inhibited the enhanced degradation of [3H]lysozyme and H2O2-treated [3H]superoxide dismutase by the proteolytic systems exposed to H2O2. Thus ascorbic acid seems to inhibit the H2O2-induced increase in ATP-independent proteolysis 1) by preventing damage to proteins by H2O2 resulting in a decreased supply of substrates for the ATP-independent degradative system and 2) by preventing activation of the proteolytic enzymes that participate in the energy-independent degradation of H2O2-treated proteins.
Subject(s)
Ascorbic Acid/pharmacology , Hydrogen Peroxide/metabolism , Muscle Proteins/metabolism , Muscles/drug effects , Adenosine Triphosphate/metabolism , Animals , Chickens , Endopeptidases/metabolism , Hydrolysis/drug effects , Male , Muramidase/metabolism , Muscles/enzymology , Muscles/metabolism , Oxidation-Reduction , Superoxide Dismutase/metabolismABSTRACT
Oxidants have been found to increase protein breakdown in erythroid cells. In skeletal muscle, phenylhydrazine decreased by 24-28% rates of protein degradation. Both H2O2 (5 mM) and glucose oxidase (0.2 U/ml) decreased by 82-88% rates of proteolysis only in skeletal muscles pretreated with sodium azide (0.25 mM) to inactivate endogenous catalase. Thus, the effect of various oxidants on protein breakdown may differ depending on the cell or tissue type.
