Fearon C W, Rodkey J A, Abeles R H
Biochemistry. 1982 Aug 3;21(16):3790-4. doi: 10.1021/bi00259a011.
Inactivation of gamma-cystathionase by beta, beta, beta-trifluoroalanine, a suicide inactivator of the enzyme, results in covalent labeling of an amino group of the protein [Silverman, R. B., & Abeles, R. H. (1977) Biochemistry 16, 5515-5520]. We have established that this modified amino function is the epsilon-NH2 group of a lysine residue. A heptapeptide which includes this modified lysine residue was isolated, and its sequence was found to be Cys-Ser-Ala-Thr-Lys-Tyr-Met. The amino acid sequence was the same as that determined for peptides containing the active-site lysine residue which forms a Schiff base with pyridoxal phosphate. Therefore the epsilon-NH2 group of the active-site lysine which binds pyridoxal phosphate is capable of interacting with the beta carbon of trifluoroalanine, and presumably the beta carbon of normal substrates. We therefore propose that this lysine residue may function as a proton-transfer agent in the reactions catalyzed by gamma-cystathionase.
β,β,β-三氟丙氨酸作为γ-胱硫醚酶的自杀性失活剂，使该酶失活，导致蛋白质的一个氨基发生共价标记[西尔弗曼，R. B.，& 阿贝莱斯，R. H.（1977年）《生物化学》16，5515 - 5520]。我们已确定这个被修饰的氨基官能团是一个赖氨酸残基的ε-NH₂基团。分离出了一个包含这个被修饰赖氨酸残基的七肽，其序列为半胱氨酸 - 丝氨酸 - 丙氨酸 - 苏氨酸 - 赖氨酸 - 酪氨酸 - 甲硫氨酸。氨基酸序列与含有与磷酸吡哆醛形成席夫碱的活性位点赖氨酸残基的肽段所确定的序列相同。因此，与磷酸吡哆醛结合的活性位点赖氨酸的ε-NH₂基团能够与三氟丙氨酸的β-碳相互作用，大概也能与正常底物的β-碳相互作用。所以我们提出，这个赖氨酸残基可能在γ-胱硫醚酶催化的反应中作为质子转移剂发挥作用。
