A CIRCULAR DICHROIC STUDY OF THE INTERACTION OF INSULIN A AND B CHAINS

It has been shown previously that the S-thiomethyl forms of the insulin A and B chains interact in solution leading to a partial transfer of Tyr side chains from hydrophilic to hydrophobic environments. In the present work, a circular dichroic study has indicated that the α-helix contents of the chains show a gradual increase upon mixing of the chains reaching completion in about 2h. The separated S-thiomethyl protected chains contain some ordered structure (A: α=15%, β=27%: B: α=22%, β=23%). Contrary to reports in the literature, the reduced chains also show some ordered structure and upon mixing of the reduced chains, the α-helix content also shows some increase. The ordered structure of the reduced chains decrease with increasing concentrations of dithiothreitel and in presence of a large excess of DTT both the reduced chains have very little, if any, α-helix structure. These latter results are in accord with those of Wu and Yang. In agreement with the results obtained previously with ultravio     

胰岛素A和B链相互作用的圆二色性研究

本文报道以圆二色性方法在相同条件下测得S-硫甲基型A链的α螺旋、β折迭的含量为15％及27％;B链为22％,23％;A和B链混合后为24％,26％。表明A和B链相混后肽链构象有一定调整,α螺旋含量有所增加。以还原型A及B链进行实验,也得到类似结果。加入二巯基苏糖醇明显减少A及B链的有序成分。上述结果表明胰岛素A及B链有一定二级结构;在能重组成胰岛素的最适条件下,A及B链相混后,因次级键相互作用,两肽链构象有一定调整,有序程度有所提高。