Kinetic studies of L-aspartase from Escherichia coli: substrate activation.
Kinetic studies of L-aspartase from Escherichia coli: substrate activation.
复制标题
大肠杆菌 L-天冬氨酸酶的动力学研究：底物激活。
DOI：
10.1021/bi00354a016
复制
发表时间：
1986
期刊：
影响因子：
2.9
通讯作者：
Viola,RE
中科院分区：
文献类型：
--
作者：
Karsten,WE;Gates,RB;Viola,RE
阿克伦大学化学系，阿克伦，俄亥俄州44325接收于1985年6月21日摘要：在从富马酸盐和氨生产天冬氨酸的过程中，观察到来自大肠杆菌的L-天冬氨酸酶具有时滞。该时间滞后是pH依赖性的，在pH 7.0以下观察到很少的滞后，而在pH 8.0以上观察到非常广泛的滞后。这一时间滞后也被认为是依赖于底物和二价金属离子的浓度和L-精氨酸酶的蛋白水解的程度。观察到的滞后，在胺化方向上检查的反应中，已被发现是相关的非线性动力学在higherpH值的脱氨基方向。这两种现象是一致的一个模型，其中有一个单独的激活位点的底物，L-天冬氨酸，这是不同的酶的活性位点。该位点被底物或各种底物类似物占据，消除了非线性和时滞。在活性位点不结合的天冬氨酸的D异构体可以在这个新鉴定的激活剂位点结合。
Department of Chemistry, University of Akron, Akron, Ohio 44325 Received June 21, 1985 abstract: The enzyme L-aspartase from Escherichia coli was observed to have a time lag during the production of aspartic acid from fumarate and ammonia. This time lag is pH dependent, with little lag observed below pH 7.0 and a very extensive lag observed above pH 8.0. This time lag was also found to be dependent on both substrate and divalent metal ion concentrations and on the degree of proteolysis of L-aspartase. The observed lag, in the reaction examined in the amination direction, has been found to be correlated with the nonlinear kinetics seen at higherpH in the deamination direction. Both phenomena are consistent with a model in which there is a separate activator site for the substrate, L-aspartic acid, that is distinct from the enzyme active site. Occupation of this site by the substrate, or by various substrate analogues, eliminates both the nonlinearity and the time lag. The D isomer of aspartic acid, which does not bind at the active site, can bind at this newly identified activator site.