title: Stereospecificity of sodium borohydride reduction of tyrosine decarboxylase from Streptococcus faecalis.
abstract: Sodium boro[3H]hydride reduction of tyrosine decarboxylase from Streptococcus faecalis followed by complete hydrolysis of the enzyme produces epsilon-[3H]pyridoxyllysine. Degradation of this material to [4'-3H]pyridoxamine and stereochemical analysis with apoaspartate aminotransferase shows that the re side at C-4' of the cofactor is exposed to solvent at pH 5.5 and 7.0. After binding of L-tyrosine at pH 5.5 or tyramine at pH 7.0 to the holoenzyme, sodium boro[3H]hydride reduction proceeds from the si face at C-4' of the substrate . cofactor complex. This indicates one of two conformational changes occurs upon binding of substrate; either rotation about the C-4 to C-4' bond in the cofactor or rotation about the axis through the C-5 and C-5' bond.
mesh_terms: D001665:Binding Sites; D001894:Borohydrides; D013293:Enterococcus faecalis / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008239:Lysine; D010084:Oxidation-Reduction; D011485:Protein Binding; D011730:Pyridoxal; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014445:Tyrosine Decarboxylase
chemical_list: D001894:Borohydrides; D011730:Pyridoxal; D014445:Tyrosine Decarboxylase; D008239:Lysine