Chazarra S, Cabanes J, Escribano J, García-Carmona F
Departamento de Bioquímica y Biología Molecular A, Facultad de Biología, Universidad de Murcia, Spain.
Biochim Biophys Acta. 1997 May 23;1339(2):297-303. doi: 10.1016/s0167-4838(97)00012-5.
In plants, polyphenoloxidase undergoes an irreversible inactivation during the oxidation of o-diphenol to o-quinones. In the present paper, using latent polyphenoloxidase from iceberg lettuce (Lactuca sativa), in the presence of an activating agent, SDS, the kinetic parameters that characterize the enzyme during its action on the suicide substrate 4-tert-butylcatechol have been determined. The effect of pH has also been considered. It was seen that the presence of SDS in the reaction medium changed the kinetic parameters of the enzyme during suicide inactivation, this phenomenon depended on the SDS concentration up to saturating concentrations. Variations were also observed in the kinetic parameters at pH values below 5 where SDS provoked inactivation of the enzyme. This differing kinetic behaviour during suicide inactivation in the presence of SDS may be caused by the conformational changes provoked by SDS in the enzyme in latent state. Thus, polyphenoloxidases showing suicide inactivation would present an enzymatic activity resulting from the balance between the activation process and suicide inactivation.
在植物中，多酚氧化酶在邻二酚氧化为邻醌的过程中会发生不可逆失活。在本文中，使用来自卷心莴苣（Lactuca sativa）的潜在多酚氧化酶，在活化剂十二烷基硫酸钠（SDS）存在的情况下，测定了该酶作用于自杀底物4-叔丁基邻苯二酚时的动力学参数。同时也考虑了pH的影响。结果发现，反应介质中SDS的存在改变了自杀失活过程中酶的动力学参数，这种现象取决于SDS浓度直至饱和浓度。在pH值低于5时，SDS会引发酶的失活，此时动力学参数也会发生变化。在SDS存在下自杀失活过程中这种不同的动力学行为可能是由SDS在潜在状态的酶中引发的构象变化所导致的。因此，表现出自杀失活的多酚氧化酶将呈现出由活化过程和自杀失活之间的平衡所产生的酶活性。
