作者:Hidehiko Kumagai、Hideyuki Suzuki、Hiroki Shigematsu、Tatsurokuro Tochikura
DOI:10.1080/00021369.1989.10869692
日期:1989.9
An enzyme that catalyzes the synthesis of S-carboxymethyl- l-cysteine from 3-chloro- l-alanine (3-Cl-Ala) and thioglycolic acid was found in Escherichia coli W3110 and was designated as S- carboxymethyl-l-cysteine synthase. It was purified from the cell-free extract to electrophoretic homogeneity and was crystallized. The enzyme has a molecular weight of 84,000 and gave one band corresponding to a molecular weight of 37,000 on SDS-polyacrylamide gel electrophoresis. The purified enzyme catalyzed the β-replacement reactions between 3-CI-AIa and various thiol compounds. The apparent Km values for 3-Cl-Ala and thioglycolic acid were 40 mM and 15.4 mM. The enzyme showed very low activity as to the α,β-elimination reaction with 3-Cl-Ala and l-serine. It was not inactivated on the incubation with 3-Cl-Ala. The absorption spectrum of the enzyme shows a maximum at 412 nm, indicating that it contains pyridoxal phosphate as a cofactor. The N-terminal amino acid sequence was determined and the corresponding sequence was detected in the protein sequence data bank, but no homogeneous sequence was found.
在大肠杆菌 W3110 中发现了一种催化从 3-氯- l-丙氨酸(3-Cl-Ala)和巯基乙酸合成 S-羧甲基-l-半胱氨酸的酶,该酶被命名为 S-羧甲基-l-半胱氨酸合成酶。它从无细胞提取物中纯化到电泳纯度,并进行了结晶。该酶的分子量为 84,000,并在 SDS-聚丙烯酰胺凝胶电泳中显示出一个对应于 37,000 的带。纯化后的酶催化了 3-Cl-Ala 与多种硫醇化合物之间的β取代反应。3-Cl-Ala 和巯基乙酸的表观 Km 值分别为 40 mM 和 15.4 mM。该酶对 3-Cl-Ala 和 l-丝氨酸的 α,β 消除反应显示出非常低的活性。在与 3-Cl-Ala 孵育后并未失活。该酶的吸收光谱在 412 nm 处显示出最大值,表明它含有作为辅因子的磷酸吡哆醛。N 末端氨基酸序列已被确定,对应的序列在蛋白质序列数据库中被检出,但没有找到同源序列。