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

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 (3S)-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.