Effects of 5,5′‐Dithiobis‐(2‐Nitrobenzoic Acid) on Opiate Binding to Both the Membrane‐Bound Receptor and the Partially Purified Opiate Receptor

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Abstract
Pretreatment of partially purified opiate receptor from rat brains with 5,5''-dithiobis-(2-nitrobenzoic acid) (DTNB) decreased opiate agonist binding more effectively than that of antagonist. This agent, at a concentration that inhibits only 3H-agonist binding, increased the IC50 [concentration producing 50% inhibition] values of agonists but not those of antagonists. Similar effects DTNB were observed on opiate binding to the membrane-bound receptor that are in good agreement with the published data. There was an excellent correlation between the IC50 values of the 2 different preparations. However, opiate binding to the partially purified receptor was about 1000-fold more sensitive to DTNB than binding to this membrane-bound receptor. Dithiothreitol, a sulfide bond reducing agent, reversed the effects of DTNB on the opiate binding.