Stole E, Seddon A P, Wellner D, Meister A
Department of Biochemistry, Cornell University Medical College, New York, NY 10021.
Proc Natl Acad Sci U S A. 1990 Mar;87(5):1706-9. doi: 10.1073/pnas.87.5.1706.
gamma-Glutamyl transpeptidase [(5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2], an enzyme of major importance in glutathione metabolism, was inactivated by treating it with L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-[3-14C]isoxazoleacetic acid. This selective reagent binds stoichiometrically to the enzyme; more than 90% of the label was bound to its light subunit. Enzymatic digestion of the light subunit gave a 14C-labeled peptide that corresponds to amino acid residues 517-527 of the enzyme and two incomplete digestion products that contain this labeled peptide moiety. The radioactivity associated with this peptide was released with threonine-523 during sequencing by the automated gas-phase Edman method. The light subunit contains 14 other threonine residues and a total of 19 serine residues; these were not labeled. Threonine-523 is situated in the enzyme in an environment that greatly increases its reactivity, indicating that other amino acid residues of the enzyme must also participate in the active-site chemistry of the enzyme.
γ-谷氨酰转肽酶[（5-谷氨酰基）-肽：氨基酸5-谷氨酰基转移酶，EC 2.3.2.2]，一种在谷胱甘肽代谢中至关重要的酶，用L-（αS，5S）-α-氨基-3-氯-4,5-二氢-5-[3-¹⁴C]异恶唑乙酸处理后被灭活。这种选择性试剂与该酶以化学计量比结合；超过90%的标记物与它的轻亚基结合。对轻亚基进行酶切得到一个¹⁴C标记的肽段，其对应于该酶的氨基酸残基517 - 527以及两个含有此标记肽段部分的不完全消化产物。在通过自动气相埃德曼法测序过程中，与该肽段相关的放射性在苏氨酸-523处被释放。轻亚基还含有14个其他苏氨酸残基和总共19个丝氨酸残基；这些残基未被标记。苏氨酸-523在酶中的所处环境极大地增加了其反应活性，这表明该酶的其他氨基酸残基也必定参与了酶的活性位点化学过程。
