巯基导向试剂对鸡肝甲羟戊酸5-二磷酸脱羧酶的失活作用：功能性二硫醇的证据。

Inactivation of chicken liver mevalonate 5-diphosphate decarboxylase by sulfhydryl-directed reagents: evidence of a functional dithiol.

作者信息

Alvear M, Jabalquinto A M, Cardemil E

机构信息

Departamento de Química, Facultad de Ciencia, Universidad de Santiago de Chile, Chile.

出版信息

Biochim Biophys Acta. 1989 Jan 19;994(1):7-11. doi: 10.1016/0167-4838(89)90055-1.

DOI:10.1016/0167-4838(89)90055-1

PMID:2909257

Abstract

Chicken liver mevalonate 5-diphosphate decarboxylase (ATP:(R)-5-diphosphomevalonate carboxy-lyase (dehydrating), EC 4.1.1.33) is inactivated by methylmethanethiosulfonate and 5,5'-dithiobis(2-nitrobenzoate). The presence of the substrates ATP or mevalonate 5-diphosphate protect very effectively against inactivation. The inactivation is second order with respect to methylmethanethiosulfonate, with an inactivation rate constant of (7.6 +/- 0.1).10(-5) microM-2.s-1, implying that the modifier may be reacting with more than one thiol in the enzyme. The enzyme is also inactivated by a number of dithiol-specific reagents, suggesting the presence of a functional dithiol. The determined pKapp values for enzyme modification by methyl methanethiosulfonate and phenylarsine oxide are 7.3 +/- 0.1 and 7.6 +/- 0.3, respectively. From the data presented, it is concluded that the enzyme possesses a functional dithiol that is important for substrate binding.

摘要

鸡肝甲羟戊酸5-二磷酸脱羧酶（ATP：（R）-5-二磷酸甲羟戊酸羧基裂解酶（脱水），EC 4.1.1.33）可被甲硫基磺酸甲酯和5,5'-二硫代双（2-硝基苯甲酸）灭活。底物ATP或甲羟戊酸5-二磷酸的存在能非常有效地防止酶的灭活。就甲硫基磺酸甲酯而言，灭活反应为二级反应，灭活速率常数为（7.6±0.1）×10⁻⁵ μM⁻²·s⁻¹，这意味着修饰剂可能与酶中的多个巯基发生反应。该酶也可被多种二硫醇特异性试剂灭活，表明存在一个功能性二硫醇。甲硫基磺酸甲酯和氧化苯胂对酶修饰所测定的表观pK值分别为7.3±0.1和7.6±0.3。根据所提供的数据，得出结论：该酶拥有一个对底物结合很重要的功能性二硫醇。