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：1980
卷号：77
期号：2
页码：795-798
DOI：10.1073/pnas.77.2.795
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The three exposed tyrosines of RNase A have been converted to nitrotyrosines by reaction with tetranitromethane, and the changes in the ionization properties of these nitrotyrosines have been used to follow the kinetics of unfolding of the nitrated protein. It is found that the nitrotyrosines not only are sensitive to the overall disruption of the protein structure, which occurs in a faster reaction, but also serve as reporter groups for the slower reaction which takes place in the unfolded state. This slower reaction corresponds to the formation of the slow-refolding species of the unfolded protein. The kinetic properties of the slower reaction--guanidine-dependence of the rate and activation ethalpy--are similar to those of the proline cis-trans isomerization in a model peptide determined in the same conditions. It is concluded that proline cis-trans isomerization is indeed the rate-limiting factor for the formation of the slow-refolding species. Because the influence of proline cis-trans isomerization on the properties of the nitrotyrosines in the unfolded protein is probably due to a local effect, it is suggested that most of the optical changes observed during this slow unfolding reaction arise from the effect of the cis-trans isomerization of the Asn113-Pro114 bond on the properties of nitrotyrosine 115.
