Vederas J C, Reingold I D, Sellers H W
J Biol Chem. 1979 Jun 25;254(12):5053-7.
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.
用硼氢化钠[³H]还原粪链球菌的酪氨酸脱羧酶，然后将该酶完全水解，产生ε-[³H]吡哆醛赖氨酸。将该物质降解为[4'-³H]吡哆胺，并使用脱辅基天冬氨酸转氨酶进行立体化学分析，结果表明，在pH 5.5和7.0时，辅因子C-4'位的残基暴露于溶剂中。在pH 5.5时L-酪氨酸或在pH 7.0时酪胺与全酶结合后，硼氢化钠[³H]从底物-辅因子复合物的C-4'位的si面进行还原。这表明在底物结合时发生了两种构象变化之一；要么是辅因子中C-4至C-4'键的旋转，要么是通过C-5和C-5'键的轴的旋转。
