Eberhardt Eric S, Loh Stewart N, Hinck Andrew P, Raines Ronald T
Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706.
J Am Chem Soc. 1992;114(13):5437-5439. doi: 10.1021/ja00039a072.
Racemic Ac-Gly-[β,δ-(13)C]Pro-OMe was synthesized, and the kinetics and thermodynamics of the isomerization of its prolyl peptide bond were determined in nine solvents by using NMR and IR spectroscopy. The free energy of activation is 1.3 kcal/mol larger in water than in aprotic solvents, and correlates with the ability of a solvent to donate a hydrogen bond but not with solvent polarity. These results are consistent with conventional pictures of amide resonance, which require transfer of charge between oxygen and nitrogen during isomerization. Similar medium effects may modulate the stability of planar peptide bonds in the active site of peptidyl-prolyl cis-trans isomerases (PPIases) and during the folding, function, or lysis of proteins.
合成了外消旋的Ac-Gly-[β,δ-(13)C]Pro-OMe,并通过核磁共振(NMR)和红外光谱(IR)在九种溶剂中测定了其脯氨酰肽键异构化的动力学和热力学。在水中,活化自由能比在非质子溶剂中高1.3千卡/摩尔,且与溶剂提供氢键的能力相关,而与溶剂极性无关。这些结果与传统的酰胺共振图景一致,该图景要求异构化过程中氧和氮之间发生电荷转移。类似的介质效应可能会调节肽基脯氨酰顺反异构酶(PPIases)活性位点中平面肽键的稳定性,以及蛋白质折叠、功能或裂解过程中的稳定性。