A CONFORMATIONAL STUDY OF GLUCAGON
A CONFORMATIONAL STUDY OF GLUCAGON
复制标题
DOI：
10.1111/j.1432-1033.1968.tb19527.x
复制
发表时间：
1968-01-01
期刊：
影响因子：
--
通讯作者：
BRADBURY, EM
中科院分区：
文献类型：
--
作者：
GRATZER, WB;BEAVEN, GH;BRADBURY, EM
胰高血糖素是由29个氨基酸残基组成的多肽，可以结晶。在稀的中性、酸性和碱性溶液中的旋光色散表明多肽链在很大程度上是随机的，但含有约1圈的[α]-螺旋，其在6 M盐酸胍中被消除。使用热差光谱、核磁共振和旋光色散的温度依赖性作为标准，似乎胰高血糖素在溶液中不具有确定的三级结构，但可被视为处于[α]-螺旋[图像]无规卷曲平衡状态，接近转变范围的高温端。在2-氯乙醇溶液中进行旋光色散测量，证明了形成高度α-螺旋构象没有空间异议，其中蛋白质大部分是螺旋状的。粗略计算表明，在pH 2的水溶液中，转变中点约为[长划线]40[度]。从质子磁共振谱的变化时，胰高血糖素从水环境转移到6 M盐酸胍，它推断，在链中的短螺旋段在水的状态下包含大部分的长脂肪族侧链，并且由于序列是已知的，它已经有可能确定这样一个片段唯一的C-末端附近。在酸溶液中静置时，粘度增加并形成双折射凝胶。沉积研究表明形成了大的聚集体。在进一步静置或加热时，出现沉淀物，其在电子显微镜下具有长纤维的外观。凝胶、固体膜和沉淀物质的红外光谱表明，在所有这些状态下，胰高血糖素都是反平行[β]链的形式。
Glucagon is a polypeptide of 29 residues, which can by crystalized. Optical rotatory dispersion in dilute neutral, acid and alkaline solution suggests that the polypeptide chain is largely random, but contains about 1 turn of [alpha]-helix, which is eliminated in 6 M guanidine hydro-chloride. Using thermal difference spectra, nuclear magnetic resonance and the temperature-dependence of the optical rotatory dispersion as criteria, it appears that glucagon possesses no defined tertiary structure in solution, but may be regarded as being in a state of [alpha]-helix [image] random coil equilibrium, near the high-temperature end of the transition range. That there is no steric objection to the formation of a highly [alpha]-helical conformation is demonstrated bv optical rotatory dispersion measurements in 2-chloroethanol solution, in which the protein becomes largely helical. A rough calculation indicates that in aqueous solution at pH 2 the transition mid-point is at about[long dash]40[degree]. From changes in the proton magnetic resonance spectrum when glucagon is transferred from an aqueous environment into 6 M guanidine hydrochloride, it is deduced that the short helical segment in the chain in the aqueous state contains most of the long aliphatic side chains, and since the sequence is known it has been possible to identify such a segment uniquely near the C-terminal end. On standing in acid solution the viscosity increases and a birefringent gel is formed. Sedimentation studies indicate the formation of large aggregates. On further standing, or warming, a precipitate appears which has the appearance of long fibrils in the electron microscope. Infrared spectra of the gel, of solid films and of the precipitated material show that in all these states the glucagon is in the form of antiparallel [beta]-chains.