Higgins K A, Craik D J, Hall J G, Andrews P R
School of Pharmaceutical Chemistry, Victorian College of Pharmacy Ltd., Parkville, Australia.
Drug Des Deliv. 1988 Jul;3(2):159-70.
The natural abundance 13C NMR spectrum of bovine insulin contains two resonances at 49.6 and 48.9 ppm which have a 7:3 intensity ratio at 298 K. Use of the DEPT spectral editing technique shows them to be of CH2 multiplicity. On the basis of their chemical shifts, which are well-resolved from other peaks, they are assigned as the C delta carbon of proline in trans and cis forms respectively. Since insulin contains only a single proline residue, the site of the isomerization can be localized at the peptide bond linking Thr-27 and Pro-28. On heating, the two peaks broaden, coalesce at 308 K, and then sharpen to yield a single peak at higher temperatures. The barrier for this process was calculated to be 64 kJ mol-1 (at the coalesce temperature), which is at the lower end of the range observed for proline isomerization in small peptides. Computer-graphic studies based on the X-ray crystal structure of insulin were used to deduce the structural implications of the cis-trans isomerism in this globular protein.
牛胰岛素的天然丰度13C NMR谱在49.6和48.9 ppm处有两个共振峰，在298 K时强度比为7:3。使用DEPT光谱编辑技术表明它们具有CH2多重性。基于它们与其他峰良好分辨的化学位移，它们分别被指定为反式和顺式脯氨酸的Cδ碳。由于胰岛素仅含有一个脯氨酸残基，异构化位点可定位在连接Thr-27和Pro-28的肽键处。加热时，这两个峰变宽，在308 K时合并，然后在更高温度下锐化产生一个单峰。该过程的势垒计算为64 kJ mol-1（在合并温度下），这处于小肽中脯氨酸异构化观察到的范围下限。基于胰岛素的X射线晶体结构的计算机图形学研究被用于推断这种球状蛋白中顺反异构化的结构意义。
