Huynh Q K, Snell E E
J Biol Chem. 1985 Mar 10;260(5):2794-7.
The two cysteinyl residues present in histidine decarboxylase from Lactobacillus 30a differ greatly in reactivity. One (class 1) reacts readily in the native state with dithiobis-(2-nitrobenzoate) with complete loss of enzyme activity; the other (class 2) reacts only after denaturation of the enzyme (Lane, R. S., and Snell, E. E. (1976) Biochemistry 15, 4175-4179). These differences in reactivity permitted use of covalent (disulfide) chromatography to isolate separate peptides that contain these two residues. Sequence analysis showed that the class 1 cysteinyl residue is at position 147 in a hydrophilic portion of the alpha chain (Huynh, Q. K., Recsei, P. A., Vaaler, G. L., and Snell, E. E. (1984) J. Biol. Chem. 259, 2833-2839), while the class 2 cysteinyl residue is present at position 71, adjacent to a hydrophobic portion of the same chain. Cysteinyl peptides identical with or homologous to the class 2 cysteinyl peptide of the Lactobacillus 30a enzyme were isolated from the alpha subunits of histidine decarboxylases from Lactobacillus buchneri and Clostridium perfringens, respectively. The L. buchneri enzyme also contained a peptide homologous to the class 1 cysteinyl peptide from Lactobacillus 30a. However, no corresponding peptide was present in the enzyme from C. perfringens, in which the second cysteinyl residue of the alpha chain occupies position 3, very near the essential pyruvoyl residue. This enzyme, unlike those from Lactobacillus 30a or L. buchneri, also contains one cysteinyl residue in its beta chain. Although Cys 147 is an active site residue in histidine decarboxylase from Lactobacillus 30a, the absence of a corresponding residue in the C. perfringens enzyme confirms previous indications (Recsei, P. A., and Snell, E. E. (1982) J. Biol. Chem. 257, 7196-7202) that this SH group is not essential for decarboxylase action.
来自乳酸杆菌30a的组氨酸脱羧酶中存在的两个半胱氨酰残基的反应活性差异很大。其中一个（1类）在天然状态下能与二硫代双（2-硝基苯甲酸）迅速反应，导致酶活性完全丧失；另一个（2类）仅在酶变性后才会反应（莱恩，R.S.，和斯内尔，E.E.（1976年）《生物化学》15卷，4175 - 4179页）。这些反应活性的差异使得可以利用共价（二硫键）色谱法分离出包含这两个残基的不同肽段。序列分析表明，1类半胱氨酰残基位于α链亲水区的第147位（胡恩，Q.K.，雷克西，P.A.，瓦勒，G.L.，和斯内尔，E.E.（1984年）《生物化学杂志》259卷，2833 - 2839页），而2类半胱氨酰残基位于第71位，与同一条链的疏水区相邻。分别从布氏乳酸杆菌和产气荚膜梭菌的组氨酸脱羧酶的α亚基中分离出了与乳酸杆菌30a酶的2类半胱氨酰肽相同或同源的半胱氨酰肽。布氏乳酸杆菌酶还含有一个与乳酸杆菌30a的1类半胱氨酰肽同源的肽段。然而，产气荚膜梭菌的酶中不存在相应的肽段，在该酶中α链的第二个半胱氨酰残基位于第3位，非常靠近必需的丙酮酸残基。与乳酸杆菌30a或布氏乳酸杆菌的酶不同，该酶的β链中也含有一个半胱氨酰残基。虽然半胱氨酸147是乳酸杆菌30a组氨酸脱羧酶的一个活性位点残基，但产气荚膜梭菌酶中不存在相应的残基，这证实了之前的研究结果（雷克西，P.A.，和斯内尔，E.E.（1982年）《生物化学杂志》257卷，7196 - 7202页），即这个巯基对于脱羧酶的作用并非必需。
