Oxidative deamination of amino acids by molecular oxygen with pyridoxal derivatives and metal ions as catalysts

Article abstract of DOI:10.1021/ja00017a019

The oxidative deamination of (p-sulfophenyl)glycine by Cu²⁺ and vitamin B₆ coenzymes pyridoxal 5′-phosphate or 5′-deoxypyridoxal to give (p-sulfophenyl)glyoxylie acid is described. The reaction conditions for kinetic measurements and were selected on the basis of previous equilibrium measurements of complex present in these reaction systems. The reaction occurs in two modes, stoichiometric and catalytic. The stoichiometric route involves the reaction of the amino acid Schiff base of pyridoxal 5′-phosphate or 5′-deoxypyridoxal to form the oxime of the coenzyme and the keto acid. The stotchiometric reactions, which occur moderately rapidly at room temperature in aqueous solution, become part of an overall catalytic system in which the amino acid and dioxygen are converted to keto add and ammonia in the of low concentrations of coenzyme and metal ion. Spectrophotometric studies demonstrate the relatively rapid conversion of the Schiff base metal chelate to the oxime complex, which is slowly converted to additional Schiff base complex by reaction with additional amino acid Hydroxylamine, which is presumably formed in the displacement reaction, is converted to ammonia under the reaction condition employed. The concentration of the intermediate oxime complex remains relatively constant when the reaction is run in the catalytic mode. Conversion to the final products was followed by isolation of the ammonia and keto acid formed, and by the quantitative estimation of ammonia. A dioxygen-18 tracer study demonstrated that dioxygen is the source of the oxime oxygen, while the oxygen of the keto acid comes from the solvent. Mechanisms previously proposed for vitamin B₆ and metal ion catalyzed amino oxidation are discussed, and a selection is made on the of ¹⁸O₂ labeling of the hydroxylation product.