The subunit structure of human thyroxine-binding prealbumin.
The subunit structure of human thyroxine-binding prealbumin.
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人甲状腺素结合前白蛋白的亚基结构。
DOI：
10.1016/s0021-9258(18)61836-8
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发表时间：
1971
期刊：
影响因子：
--
通讯作者：
S. Nilsson
中科院分区：
文献类型：
--
作者：
L. Rask;P. A. Peterson;S. Nilsson
采用硫酸铵分级分离、二乙氨基乙基葡聚糖凝胶层析和凝胶过滤等方法从人血浆中分离前白蛋白。对高度纯化的蛋白质进行定量氨基酸分析，结果显示每个前白蛋白分子至少含有140个氨基酸残基。通过测定最大偏差分数曲线中的最小值，发现前白蛋白的最小分子量为15，500。通过沉降平衡超离心法测定分子量，结果为62，500 ± 2，200。这些结果表明，前白蛋白是由四个亚基。用凝胶色谱法在盐酸6 M胍中测定前白蛋白的分子量，其值约为16，000。用肽图技术检测了前白蛋白的胰蛋白酶消化物，检测到的肽数（15 ~ 19）与由四条相同链组成的前白蛋白四聚体的氨基酸组成计算的赖氨酸和精氨酸残基的总数一致。蛋白质的NH 2-末端序列被证明是唯一的Gly-Pro。前白蛋白，还原和14 C-羧甲基化，进行胰蛋白酶消化，和放射性被用来跟踪和分离含半胱氨酸的肽。只有一种肽含有放射性，对该肽的分析显示了独特的序列Gly-Pro-Ser-Met-Val-Cys（Cm）-Lys。这些数据加强了前白蛋白是由相同的亚基组成的观点，前白蛋白四聚体的解离模式进行了研究，在不同浓度的盐酸胍的沉降平衡超离心。局部重量和数均分子量的测定与参与化学平衡的三种物质一致，即前白蛋白亚基的单体、二聚体和四聚体。
Prealbumin was isolated from human plasma by ammonium sulfate fractionation, chromatographic separations on diethylaminoethyl-Sephadex, and gel filtrations. The highly purified protein was subjected to quantitative amino acid analyses, which showed a minimum of 140 amino acid residues per prealbumin molecule. By determination of the minimum in the curves for the fraction of maximum deviation it was found that the minimum molecular weight for prealbumin was 15,500. Molecular weight determinations by sedimentation equilibrium ultracentrifugations gave a value of 62,500 ± 2,200. These results indicate that prealbumin is composed of four subunits. Molecular weight determinations by gel chromatography in 6mguanidine hydrochloride gave values of about 16,000 for prealbumin. By this method it was shown that the subunits are held together by noncovalent bonds.A trypsin digest of prealbumin was examined by peptide-mapping techniques and the number of peptides (15 to 19) detected was in good agreement with the total number of lysine and arginine residues calculated from the amino acid composition of a prealbumin tetramer consisting of four identical chains. The NH2-terminal sequence of the protein was shown to be uniquely Gly-Pro.Prealbumin, reduced and14C-carboxymethylated, was subjected to tryptic digestion, and the radioactivity was used to trace and isolate the cysteine-containing peptides. Only one peptide contained radioactivity, and analysis of this peptide revealed the unique sequence Gly-Pro-Ser-Met-Val-Cys(Cm)-Lys. These data strengthen the view that preal-bumin is composed of identical subunits.The mode of dissociation of the prealbumin tetramer was investigated by sedimentation equilibrium ultracentrifugation in various concentrations of guanidine hydrochloride. Determinations of local weight and number average molecular weights were consistent with three species being involved in chemical equilibrium,i.e.monomers, dimers, and tetramers of the prealbumin subunits.