Oxidative Modification of Glutamine Synthetase: Covalent and Conformational Changes Which Control Susceptibility to Proteolysis
Mixed function oxidation of proteins has been implicated in a variety of physiologic and pathologic processes, including intracellular protein turnover, host defense activities, oxygen toxicity, and the aging process. Many key enzymes are susceptible to oxidative modification, usually with loss of catalytic activity.1 Glutamine synthetase from Escherichia coli is oxidatively modified by a number of enzymic and non-enzymic mixed function oxidation systems.2,3 To understand the effects of oxidative modification, we have studied the covalent and non-covalent changes in glutamine synthetase which occur upon oxidative modification. Protein of varying extent of modification was prepared by timed exposure to a model system consisting of ascorbate, iron, and molecular oxygen.1,4 These modified proteins were analyzed for several covalent and conformational changes. We were particularly interested in identifying changes which correlate with increased susceptibility to proteolysis by a novel high molecular weight protease purified from rat liver.
KeywordsGlutamine Synthetase Histidine Residue Sedimentation Velocity Oxidative Modification Cation Binding Site
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