Fujii N, Momose Y, Harada K
Research Development Corporation of Japan (JRDC), Ibaraki, Japan.
Int J Pept Protein Res. 1996 Aug;48(2):118-22. doi: 10.1111/j.1399-3011.1996.tb00821.x.
We have reported that two aspartyl (Asp-151 and Asp-58) residues in alpha A-crystallin in human eye lens were inverted to the D-isomer and isomerized to beta-aspartyl residues with age. We report here the kinetics of the Asp racemization of three model peptides corresponding to fragments of alpha A-crystallin: IQTGLD151ATHAER (T18 peptide), TVLD58SGISEVR (T6 peptide) and HFSPED84LTVK (T10 peptide, as a control). The rate constants of the racemization of Asp residues in these peptides were measured at pH 7.0, at five temperatures: 50, 60, 70, 80 and 90 degrees C. From the Arrhenius equation, we estimated the activation energy (E) of racemization and the time required for the Asp D/L ratio to approximate to 1.0 (D/L ratio of Asp = 0.99) at body temperature. For the peptide T18, E = 21.4 kcal/mol and t = 13.5 yr. For the peptide T6, E = 26.8 kcal/mol and r = 49.5 yr. For the control peptide T10, E = 28.3 kcal/mol and t = 78.1 yr. The racemization rate of Asp in these three peptides is parallel to that of Asp residues in alpha A-crystallin. The racemization rate of Asp in the T18 peptide was very rapid compared to that in the other peptides. This result also reflects the racemization rate in native alpha A-crystallin.
我们曾报道，人眼晶状体中αA-晶状体蛋白的两个天冬氨酰残基（Asp-151和Asp-58）会随着年龄增长转化为D-异构体并异构化为β-天冬氨酰残基。我们在此报告对应于αA-晶状体蛋白片段的三种模型肽的天冬氨酸消旋动力学：IQTGLD151ATHAER（T18肽）、TVLD58SGISEVR（T6肽）和HFSPED84LTVK（T10肽，作为对照）。在pH 7.0、五个温度（50、60、70、80和90摄氏度）下测量了这些肽中天冬氨酸残基的消旋速率常数。根据阿伦尼乌斯方程，我们估算了消旋的活化能（E）以及在体温下天冬氨酸D/L比接近1.0（天冬氨酸的D/L比 = 0.99）所需的时间。对于T18肽，E = 21.4千卡/摩尔，t = 13.5年。对于T6肽，E = 26.8千卡/摩尔，r = 49.5年。对于对照肽T10肽，E = 28.3千卡/摩尔，t = 78.1年。这三种肽中天冬氨酸的消旋速率与αA-晶状体蛋白中天冬氨酸残基的消旋速率平行。与其他肽相比，T18肽中天冬氨酸的消旋速率非常快。该结果也反映了天然αA-晶状体蛋白中的消旋速率。
