Characterization of the slow steps in the folding of the alpha subunit of tryptophan synthase.
Characterization of the slow steps in the folding of the alpha subunit of tryptophan synthase.
复制标题
色氨酸合酶α亚基折叠缓慢步骤的表征。
DOI：
10.1021/bi00512a052
复制
发表时间：
1981
期刊：
影响因子：
2.9
通讯作者：
Matthews,CR
中科院分区：
文献类型：
--
作者：
Crisanti,MM;Matthews,CR
Mark M. Crisanti and C. Robert Matthews* abstract: The two slow phases detected by ultraviolet spectroscopy in the refolding of the urea-unfolded a subunit of tryptophan synthase have been analyzedfor their dependence on final urea concentration, pH, and temperature. The decay time of the slower of the two phases is independent of final urea concentration and pH and has an activation energy of 17.6±2.5 kcal mol'1. This behavior is consistent with the explanation that proline isomerization is the rate-limiting process in the step corresponding to this phase. The decay time for the faster phase depends on both the final urea concen-tration and the pH; the variation with pH is well described by a single protonation event with a pK of 7.6±0.3. The activation energy for this phase is 14.5±2.6 kcal mol'1. It appears that thestep corresponding to this phase is not simply related to proline isomerization. The binding of a competitive inhibitor for the a subunit, indolepropanol phosphate, during refolding displays biphasic kinetics; the decay times for the two phases are identical with those observed for the folding of the protein in theabsence of inhibitor. All of the results can be explained in terms of a folding model in which the unfolded protein exists in two kinetically different forms. These two species rapidly collapse to two intermediate forms, one of which proceeds directly to the native conformation by the pH-dependent step, with the intermediate decay time. The second intermediate must first execute a proline isomerization before proceeding to the native form.
