期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1995
卷号：92
期号：4
页码：1067-1071
DOI：10.1073/pnas.92.4.1067
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Aqueous solutions of the bovine eye lens protein gamma II (or gamma B)-crystallin at neutral pH show a gradual increase in phase separation temperature, Tph, when allowed to stand for several weeks at room temperature without reducing agents. In a typical experiment, the Tph of the protein solution (218 mg/ml) increases from 2.5 +/- 1 degree C to 32.5 +/- 1 degree C after 21 days, and a new protein species, gamma IIH, is formed. The Tph of pure gamma IIH is at least 40 degrees C higher than that of pure gamma II. The average apparent hydrodynamic radius is 36 A for gamma IIH compared to 26 A for gamma II. The molecular mass of gamma IIH is approximately 41.5 kDa compared to 20 kDa for native gamma II. Therefore, gamma IIH is probably a dimer of gamma II crystallin. gamma IIH has a lower thiol content than gamma II and is not formed in the presence of dithiothreitol. We conclude that gamma IIH is a thiol oxidation product of gamma II-crystallin and is a dimer containing an intermolecular disulfide crosslink. Thus, some oxidative modifications of protein thiol groups lead to an increase in net attractive interactions between proteins. As a result, Tph increases and protein aggregates are formed. These two microscopic changes produce the increased light scattering associated with lens opacification.
