Transamination of some sulphur- or selenium-containing amino acids by bovine liver glutamine transaminase

S-(3-aminopropyl)cysteine and Se-(3-aminopropyl)selenocysteine are deaminated by bovine liver glutamine transaminase. The corresponding alpha-keto acids, S-(3-aminopropyl)-thiopyruvic acid and Se-(3-aminopropyl)selenopyruvic acid, are produced which spontaneously cyclize to ketimine derivatives. They have been identified by comparing their UV absorption spectra and some chemical or chromatographic properties with chemically synthesized authentic samples. Also S-(2-aminoethyl)homocysteine is the substrate for the enzyme. Kinetic parameters determined in comparison to thialysine and selenalysine show that neither the presence of a sulphur or a selenium atom nor the relative position of the atom in the carbon chain appreciably affects the substrate specificity of the enzyme. However, the length of the carbon chain has some influence on it.