Structural studies of α-crystallin

作者：S G Waley · 发表于：Biochemical Journal · 年份：1965 · DOI：10.1042/bj0960722 · 被引用次数：33 · 研究领域：Connexins and lens biology、Biochemical effects in animals

1. ac-Crystallin has been isolated from the cortex of ox lens by isoelectric precipi- tation followed by chromatography on DEAE-cellulose.The amino acid composition is in agreement with that reported for oc-crystallin prepared by a different method.There is one thiol group/20 000g. of protein (20 000 is the order ofmagnitude of the sub-unit molecular weight), and disulphide bonds are absent.2. The thiol group has been alkylated with radioactive iodoacetate in the presence of urea.3. Partial acid hydrolysis of the alkylated protein gives, according to the conditions, mainly three radioactive peptides or nearly exclusively one radioactive dipeptide.The dipeptide is N-seryl-(S-carboxymethyl)cysteine, Ser-CMCys.The two other peptides are probably the tripeptides related to Ser-CMCys.4. The simplest interpretation of these results is that the sequence around the cysteine residue is a common structural feature of the sub-units of oc-crystallin.About one-third of the weight of lens is due to the proteins that it contains, and the nature and state of these proteins must be important in maintaining the clarity of the lens.The best known of the lens proteins is a-crystallin, the main constituent of the fraction precipitated at pH 5.This was the original (Morner, 1894) characteristic property defining ac-crystallin, but, since Hesselvik (1939) identified a-crystallin as the component migrating most rapidly towards the anode on electrophoresis, several preparative methods have utilized t...