Venkatesu Pannur, Lee Ming-Jer, Lin Ho-mu
Department of Chemical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 106-07, Taiwan.
Arch Biochem Biophys. 2007 Oct 1;466(1):106-15. doi: 10.1016/j.abb.2007.07.004. Epub 2007 Jul 14.
To understand trimethylamine N-oxide (TMAO) attenuation of the denaturating effects of urea or guanidine hydrochloride (GdnHCl), we have determined the apparent transfer free energies (DeltaG(tr)(')) of cyclic dipeptides (CDs) from water to TMAO, urea or GdnHCl, and also the blends of TMAO and denaturants (urea or GdnHCl) at a 1:2 ratio as well as various denaturant concentrations in the presence of 1M TMAO, through the solubility measurements, at 25 degrees C. The CDs investigated in the present study included cyclo(Gly-Gly), cyclo(Ala-Ala) and cyclo(Val-Val). The observed DeltaG(tr)(') values indicate that TMAO can stabilize the CDs while urea or GdnHCl can destabilize the CDs. Furthermore, the DeltaG(tr)(') values of the blends of TMAO with urea or GdnHCl revealed that TMAO strongly counteracted the denaturating effects of urea on CDs in all instances, however, TMAO partially counteracted the perturbing effects of GdnHCl on CDs. TMAO counteraction ability of the deleterious effects of denaturants depended on the denaturant-CDs pair. The experimental results were further used to estimate the transfer free energies (Deltag(tr)(')) of the various functional group contributions from water to TMAO, urea or GdnHCl individually and to the combinations of TMAO and the denaturants in various ratios.
为了理解氧化三甲胺（TMAO）对尿素或盐酸胍（GdnHCl）变性作用的衰减，我们通过在25℃下的溶解度测量，测定了环二肽（CDs）从水到TMAO、尿素或GdnHCl以及TMAO与变性剂（尿素或GdnHCl）以1:2比例混合的体系，还有在1M TMAO存在下不同变性剂浓度体系中的表观转移自由能（ΔG(tr)'）。本研究中所研究的环二肽包括环（甘氨酸 - 甘氨酸）、环（丙氨酸 - 丙氨酸）和环（缬氨酸 - 缬氨酸）。观察到的ΔG(tr)'值表明，TMAO可以使环二肽稳定，而尿素或GdnHCl会使环二肽不稳定。此外，TMAO与尿素或GdnHCl混合物的ΔG(tr)'值表明，在所有情况下TMAO都强烈抵消了尿素对环二肽的变性作用，然而，TMAO只是部分抵消了GdnHCl对环二肽的扰动作用。TMAO对变性剂有害作用的抵消能力取决于变性剂 - 环二肽对。实验结果还被进一步用于单独估算各种官能团从水到TMAO、尿素或GdnHCl以及从水到不同比例的TMAO与变性剂组合体系的转移自由能（Δg(tr)'）。
