title: Stereochemistry of holoaspartate transaminase after modification of the active site Lys-258.
abstract: Proton incorporation at position C4 of the substrate-coenzyme Schiff base of aspartate transaminase is a stereospecific process. After carbamylation of the active site Lys-258, the stereospecificity of the reaction in 2H2O is retained. By a correlation method, it is shown that addition occurs from the si side of the complex and the pyridoxamine phosphate produced is deuterated at position pro-S of the pyridoxamine methylene group. These results constitute a demonstration for the stereochemstry of a half-transamination process of the phosphorylated coenzyme under single turnover conditions. They also illustrate that free Lys-258 is not required to maintain stereospecificity and cast doubts on the implication of this residue as a participant in C4 proton addition during catalysis by the native form of this mammalian enzyme.
mesh_terms: D000818:Animals; D001219:Aspartate Aminotransferases / Q000378:metabolism; D001665:Binding Sites; D003903:Deuterium; D007700:Kinetics; D008239:Lysine; D009682:Magnetic Resonance Spectroscopy; D009206:Myocardium / Q000201:enzymology; D011487:Protein Conformation; D011733:Pyridoxamine; D013552:Swine
chemical_list: D011733:Pyridoxamine; D003903:Deuterium; D001219:Aspartate Aminotransferases; D008239:Lysine