Kajihara J, Enomoto M, Seya K, Sukenaga Y, Katoh K
Pharmaceuticals Group, Nippon Kayaku Co., Ltd., Tokyo.
J Biochem. 1988 Oct;104(4):638-42. doi: 10.1093/oxfordjournals.jbchem.a122525.
Recombinant human Cu2Zn2SOD expressed in Escherichia coli consisted of mainly three isomers with isoelectric points of 5.14 (A), 5.06 (B), and 4.99 (C). Each isomer was isolated by DEAE-Toyopearl chromatography and the physiochemical properties were investigated. No significant differences in chemical and spectrophotometric properties, such as specific activity, metal contents, amino acid composition, and UV and ESR spectra, were found. The result of labeling of free cysteine residues with ABD-F showed the disulfide bond to be formed between 57Cys and 146Cys in every isomer. A few differences were found in the CD spectrum around 260 nm and in the elution patterns on reverse-phase HPLC. The isoelectric points of the three isomers became the same after treatment by reduction and carboxymethylation and even after reduction only, pI of isomers tended to be at the value of component (A). These results suggest that the three isomers are identical in primary structure but slightly different in secondary or tertiary structure. These differences are probably derived from structural alterations around 111Cys.
在大肠杆菌中表达的重组人Cu2Zn2SOD主要由三种异构体组成，其等电点分别为5.14（A）、5.06（B）和4.99（C）。通过DEAE- Toyopearl色谱法分离出每种异构体，并对其理化性质进行了研究。在化学和分光光度性质方面，如比活性、金属含量、氨基酸组成以及紫外和电子顺磁共振光谱，未发现显著差异。用ABD-F标记游离半胱氨酸残基的结果表明，每种异构体中57位半胱氨酸和146位半胱氨酸之间形成了二硫键。在260nm附近的圆二色光谱以及反相高效液相色谱的洗脱模式上发现了一些差异。经还原和羧甲基化处理后，三种异构体的等电点变得相同，甚至仅经过还原处理后，异构体的pI也倾向于达到组分（A）的值。这些结果表明，这三种异构体的一级结构相同，但二级或三级结构略有不同。这些差异可能源于111位半胱氨酸周围的结构改变。
