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：1977
卷号：74
期号：11
页码：4862-4866
DOI：10.1073/pnas.74.11.4862
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Incubation of Rhodospirillum rubrum homoserine dehydrogenase (L-homoserine:NAD+ oxidoreductase, EC 1.1.1.3 ) with p-mercuribenzoate (PMB) in the presence of 0.2 M KCl and 2 mM L-threonine resulted in complete loss of enzyme activity. Upon removal of excess PMB, KCl, and L-threonine, a time-dependent recovery of enzyme activity was observed in 25 mM phosphate/I mM EDTA buffer, pH 7.5. Circular dichroism studies indicated that the transition from inactive to reactivated form of the enzyme was accompanied by a conformational change in the protein. Experiments with [14C]PMB revealed loss of enzyme-bound radioactivity during reactivation. Increase in ionic strength of the phosphate buffer and/or addition of L-threonine, leading to enzyme aggregation, decreased the rate of enzyme reactivation, aggregated enzyme that remained inactive retained [14C]PMB on the enzyme. Sulfhydryl titration of various forms of the enzyme suggested a preferential release of PMB from a sulfhydryl group essential to enzymic activity. We conclude that reactivation of the inactive enzyme is due to dissociation of PMB from an "active-site" sulfhydryl group and that changes in the protein structure influence the rate of dissociation of the enzyme-PMB complex.
