Deuterium isotope effects in mechanistic studies of biotransformations of l-tyrosine and <i>p</i>-hydroxyphenylpyruvic acid catalyzed by the enzyme l-phenylalanine dehydrogenase

Abstract The mechanisms of the reversible oxidative deamination of l -tyrosine to p -hydroxyphenylpyruvic acid and reductive amination of phenylpyruvic acid to l -phenylalanine, both catalyzed by the enzyme l -phenylalanine dehydrogenase (PheDH, EC 1.4.1.20), were investigated using the kinetic isotope effect (KIE) and solvent isotope effect (SIE) methods. The values of deuterium kinetic effects in the 2-position of l -tyrosine and KIE in the (3 S )-position of phenylpyruvic acid and solvent isotope effects for both reactions were determined using the non-competitive spectrophotometric method. Some mechanistic details of these biotransformations were discussed.