Changes in the hydrogen exchange kinetics of Escherichia coli aspartate transcarbamylase produced by effector binding and subunit association.
Changes in the hydrogen exchange kinetics of Escherichia coli aspartate transcarbamylase produced by effector binding and subunit association.
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效应子结合和亚基缔合产生的大肠杆菌天冬氨酸转氨甲酰酶氢交换动力学的变化。
DOI：
10.1073/pnas.78.11.6759
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发表时间：
1981
影响因子：
11.1
通讯作者：
Allewell,NM
中科院分区：
文献类型：
--
作者：
Lennick,M;Allewell,NM
如通过氚交换监测的，溶剂对天冬氨酸转氨甲酰酶（天冬氨酸氨甲酰转移酶，氨甲酰磷酸：L-天冬氨酸氨甲酰转移酶，EC 2.1.3.2）的可及性的大的变化由底物和底物类似物与催化亚基（c3）的结合、核苷三磷酸与调节亚基（r2）的结合以及亚基缔合引起。在每一种情况下，汇率都有所下降，尽管程度不同。琥珀酸盐在氨甲酰磷酸盐存在下，阻滞从c3的交换不超过单独的氨甲酰磷酸盐，并且小于N-膦酰基乙酰基-L-天冬氨酸盐，一种双底物类似物。CTP比ATP产生的r2交换率变化更大;然而，CTP和ATP在相同程度上加速了c3的交换。由底物类似物和核苷三磷酸与天然酶（c6 r6）结合引起的交换动力学变化要小得多。氨甲酰基磷酸盐，有或没有琥珀酸盐，延迟交换只有轻微的，而双底物类似物有一个有点大的影响。重组酶，其中只有C3是氚标记的实验表明，活性位点配体产生的溶剂可及性的变化主要局限于C3。CTP和ATP均不显著改变从c6 r6的总体交换速率。在只标记一个亚基的实验中，排除了两种亚基发生相反变化的可能性。连接和亚基协会的非加性效应意味着一组共同的两个过程的响应质子，并建议，他们不仅在功能和功能上，但也动态连接。
Large changes in solvent accessibility to aspartate transcarbamylase (aspartate carbamoyltransferase, carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2), as monitored by tritium exchange, result from binding of substrates and substrate analogs to the catalytic subunit (c3), binding of nucleoside triphosphates to the regulatory subunit (r2), and subunit association. Rates of exchange are reduced in each of these cases, although to different degrees. Succinate, in the presence of carbamoyl phosphate, retards exchange from c3 no more than carbamoyl phosphate alone, and less than N-phosphonacetyl-L-aspartate, a bisubstrate analog. Larger changes in rates of exchange from r2 are produced by CTP than by ATP; however, both CTP and ATP accelerate exchange from c3 to the same extent. The changes in the kinetics of exchange that result from binding of both substrate analogs and nucleoside triphosphates to the native enzyme (c6r6) are much smaller. Carbamoyl phosphate, with or without succinate, retards exchange only slightly, while the bisubstrate analog has a somewhat larger effect. Experiments with reconstituted enzyme, in which only c3 is tritium labeled, indicate that changes in solvent accessibility produced by active site ligands are largely confined to c3. Neither CTP nor ATP alters the overall rate of exchange from c6r6 significantly. The possibility of opposing changes in the two types of subunits was ruled out in experiments in which only one subunit was labeled. The nonadditive effects of ligation and subunit association imply a set of responsive protons common to both processes and suggest that they are linked not only thermodynamically and functionally but also dynamically.