Evidence for the participation of disulfide and sulfhydril groups in the specific binding of [3H]prazosin in cerebral cortex.

The tritiated alpha 1 antagonist prazosin [3H]PRZ binds specifically and with high affinity to postsynaptic adrenoceptors in membrane preparations from cerebral cortex. Since adrenoceptors are of protein nature, it was of interest to investigate the possible role of disulfide (--SS--) and sulfhydril (--SH) groups in the binding of [3H]PRZ. Pretreatment of the membranes with the disulfide and sulfhydryl reactives DL-Dithiothreitol, L-Dithiothreitol, Dithioerythritol or 5',5'-Dithiobis-(2-nitrobenzoic acid) (DTNB), alone or in combination with the alkylating agent N-Methylmaleimide (NMM), decreased specific [3H]PRZ binding, with minor changes in the non-specific counts. Saturation experiments revealed that all these reagents reduced the affinity of the binding site for [3H]PRZ, as judged by the Kd 25 degrees C, but only the alkylating agent NMM and the oxydizing reagent DTNB produced in addition to the increase in Kd, a decrease of the maximum binding capacity (Bmax). The present results provide evidence for a participation of --SS-- and/or --SH groups in the recognition site of the alpha 1-adrenoceptor of cerebral cortex.