Preparation of sulfur and selenium amino acids with microbial pyridoxal phosphate enzymes

Abstract

Publisher Summary A number of pyridoxal 5'-phosphate-dependent enzymes are applied to the preparation of sulfur- and selenium-bearing amino acids. Enzymatic procedures are established for the synthesis of D- and L-cysteine with bacterial pyridoxal phosphate enzymes. This chapter describes enzymatic methods for the syntheses of L- selenocystine, L-selenohomocystine, S-substituted L-homocysteines, S-substituted L-cysteines, and Se-substituted L-selenocysteines. The procedure for the preparation of S-substituted L-homocysteines with L-methionine γ-lyase is described. L-methionine γ-lyase is a versatile pyridoxal phosphate enzyme. Various S-substituted L-homocysteines can be prepared by the enzyme-catalyzed γ-replacement reaction. The chapter also describes the preparation of S-substituted L-cysteines and Se-substituted L-selenocysteines with tryptophan synthase. Tryptophan synthase is a pyridoxal phosphate enzyme with multiple catalytic functions. The enzyme is applicable to the preparation of S-substituted L-cysteines and Se-substituted L-selenocysteines. The chapter also includes the simple methods for the specific labeling of sulfur amino acids with deuterium and tritium. These methods are based on the hydrogen exchange reactions catalyzed by L-methionine γ-lyase.