Trimethylamine-N-oxide counteracts urea effects on rabbit muscle lactate dehydrogenase function:: A test of the counteraction hypothesis
Trimethylamine-N-oxide counteracts urea effects on rabbit muscle lactate dehydrogenase function:: A test of the counteraction hypothesis
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DOI：
10.1016/s0006-3495(98)77972-x
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发表时间：
1998-05-01
影响因子：
3.4
通讯作者：
Bolen, DW
中科院分区：
文献类型：
--
作者：
Baskakov, I;Wang, AJ;Bolen, DW
鲨鱼和鳐鱼细胞中的三甲胺-N-氧化物（TMAO）被认为可以抵消这些动物细胞内高浓度尿素的有害影响。据推测，TMAO 具有抵消尿素对蛋白质结构和功能的影响的通用能力，无论该蛋白质是否实际上在这两种溶质存在的情况下进化。兔肌肉乳酸脱氢酶（LDH）在任何一种溶质存在的情况下都不会进化，这里用它来测试抵消假设的有效性。以丙酮酸为底物，结果表明尿素增加其 K-m 以及丙酮酸和 NADH 的组合 K-m，TMAO 降低，并且在尿素：TMAO 1:1 和 2:1 混合物中，K-m 值基本上等于不存在两种溶质时获得的 K-m 值。相反，作为底物的 NADH 的 k(cat) 和 K-m 值不受尿素、TMAO 或尿素:TMAO 混合物的干扰。所有这些效应都与尿素对 LDH 动力学参数影响的 TMAO 抵消作用一致，支持了抵消作用是溶剂系统的特性并且与蛋白质的进化历史无关的前提。
Trimethylamine-N-oxide (TMAO) in the cells of sharks and rays is believed to counteract the deleterious effects of the high intracellular concentrations of urea in these animals. It has been hypothesized that TMAO has the generic ability to counteract the effects of urea on protein structure and function, regardless of whether that protein actually evolved in the presence of these two solutes. Rabbit muscle lactate dehydrogenase (LDH) did not evolve in the presence of either solute, and it is used here to test the validity of the counteraction hypothesis. With pyruvate as substrate, results show that its K-m and the combined K-m of pyruvate and NADH are increased by urea, decreased by TMAO, and in 1:1 and 2:1 mixtures of urea:TMAO the K-m values are essentially equivalent to the K-m values obtained in the absence of the two solutes. In contrast, values of k(cat) and the K-m for NADH as a substrate are unperturbed by urea, TMAO, or urea:TMAO mixtures. All of these effects are consistent with TMAO counteraction of the effects of urea on LDH kinetic parameters, supporting the premise that counteraction is a property of the solvent system and is independent of the evolutionary history of the protein.