Kim Y, Shields J E
Parenteral Products Research and Development, Eli Lilly and Company, Indianapolis, IN 46285.
Biochem Biophys Res Commun. 1992 Jul 31;186(2):1115-20. doi: 10.1016/0006-291x(92)90862-f.
Zinc insulin hexamer has been shown to undergo a phenol-induced T6 to R6 conformational transition in solution. Our circular dichroic (CD) studies demonstrate that insulin undergoes pH-dependent conformational changes over the pH range of 6-10 in the T-state and in the R- state. In order to determine which specific amino acid residues may be responsible for these pH-dependent changes, a series of insulin analogs were utilized. In the T-state, the pH dependent CD changes monitored in the far UV region have a pK of 8.2 and appear to be related to the titration of the A1-Gly amino group. Using the near UV CD a second pH-dependent conformational change was detected with a pK of 7.5 in the T-state. 1H N.M.R. studies suggest that B5-His may be responsible for this conformational transition. In the presence of m-cresol (R-state), the pK value was found to be 6.9. During this titration, the increased ellipticity for the R-state is diminishing as pH decreases from pH 8 to 6, and no difference in ellipticity was observed at 255 nm between T- and R-states at pH 6. Therefore, this may be due to the transition from the R back to the T-state.
锌胰岛素六聚体已被证明在溶液中会发生苯酚诱导的从T6到R6的构象转变。我们的圆二色性（CD）研究表明，胰岛素在T态和R态下，在pH值6 - 10范围内会发生pH依赖性的构象变化。为了确定哪些特定氨基酸残基可能导致这些pH依赖性变化，我们使用了一系列胰岛素类似物。在T态下，在远紫外区域监测到的pH依赖性CD变化的pK值为8.2，似乎与A1 - Gly氨基的滴定有关。使用近紫外CD，在T态下检测到第二个pH依赖性构象变化，其pK值为7.5。1H核磁共振研究表明，B5 - His可能是这种构象转变的原因。在间甲酚（R态）存在的情况下，发现pK值为6.9。在这个滴定过程中，随着pH从8降至6，R态增加的椭圆率逐渐减小，在pH 6时，T态和R态在255 nm处的椭圆率没有差异。因此，这可能是由于从R态转变回T态所致。
