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：1975
卷号：72
期号：6
页码：2404-2407
DOI：10.1073/pnas.72.6.2404
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The role of SH groups in opiate-receptor interactions has been further examined. In activation by N-ethylmaleimide of sterospecific opiate binding by rat brain membrane fractions follows pseudo-first order kinetics and exhibits strong temperature dependence. The kinetics indicate that alkylation of a single SH group suffices to block opiate binding. Considerable protection from SH group inactivation is observed when treatment with N-ethylmaleimide is carried out in the presence of an opiate or an antagonist, suggesting close proximity of the SH group to the opiate binding site. The rate of inactivation of receptor binding by N-ethylmaleimide is markedly slower in buffers containing 100 mM NaCl (t1/2 equals 30 plus or minus 1.4 min) than in sodium-free buffers (t1/2 equals 10 plus or minus 1.0 min). Since the rate of alkylation of model SH compounds is unaffected by sodium ions, this protection seems best explained by a conformational change in the receptors that renders the SH groups less accessible to alkylation. The rate of inactivation is not affected by K+, Rb+, or Cs+ and only slightly by Li+. This cation specificity as well as the concentration-response to Na+ are remarkably similar to those previously shown to lead to increased antagonist and decreased agonist binding. We suggest that the same conformational change is involved in the two phenomena.
