In the spatial structure of tyrosine phenol-lyase, the Ser51 residue is located in the active site of the enzyme. The replacement of Ser51 with Ala by site-directed mutagenesis led to a decrease of the k_cat/K_m parameter for reactions with l-tyrosine and 3-fluoro-l-tyrosine by three orders of magnitude, compared to wild type enzyme. For the elimination reactions of S-alkylcysteines, the values of k_cat/K_m decreased by an average of two orders of magnitude. The results of spectral studies of the mutant enzyme gave evidence for a considerable change of the chiral properties of the active site as a result of the replacement. Fast kinetic studies for the complexes of the mutant form with competitive inhibitors allowed us to conclude that the Ser51 residue interacts with the side chain amino group of Lys257 at the stage of C-α-proton abstraction. This interaction ensures the correct orientation of the side chain of Lys257 accepting the C-α-proton of the external aldimine and stabilizes its ammonium form. Also, it is probable that Ser51 takes part in formation of a chain of hydrogen bonds which is necessary to perform the transfer of the C-α-proton to the C-4′-position of the leaving phenol group in the reaction with the natural substrate.

在酪氨酸酚裂解酶的空间结构中，Ser51残基位于酶的活性位点。与野生型酶相比，通过定点诱变用Ala取代Ser51导致与l-酪氨酸和3-氟-1-酪氨酸反应的k _cat / K _m参数降低了三个数量级。对于S-烷基半胱氨酸的消除反应，k _cat / K _m的值平均下降了两个数量级。突变酶的光谱研究结果表明，由于置换，活性位点的手性有相当大的变化。快速突变体形式与竞争性抑制剂的配合物的动力学研究使我们得出结论，在C-α质子提取阶段，Ser51残基与Lys257的侧链氨基相互作用。这种相互作用确保了Lys257的侧链的正确取向，该Lys257的侧链接受外部醛亚胺的C-α质子并稳定了其铵盐形式。同样，Ser51可能参与形成氢键链，这是在与天然反应中将C-α质子转移到剩下的酚基团的C-4'位置所必需的基质。