MOLECULAR PHARMACOLOGY, 44:62-69 Direct Measurements of In Situ Interactions of Rat Brain Opiold

The interactions of rat brain cortical opioid receptors with the guanine nucleotide-binding protein (G protein) G0 were probed in membranes by examining the ability of selective antipeptide anti-G protein antisera to disrupt receptor-G protein interactions. This was measured both by antibody-induced alterations in the char-acteristics of agonist binding to and 5 receptor binding sites and by antibody attenuation of opioid stimulation of high affinity GTPase activity. Antisera to the amino-terminal 1 6 amino acids (ON1), amino acids 22-35 (IM1), and the carboxyl-terminal de-capeptide (0C2) of forms of G0,, were able to selectively immu-noprecipitate G0 from rat cortical membranes. Both antisera 0C2 and ON1 were able to immunoprecipitate G0,, quantitatively. Preincubation of rat cortical membranes with an lgG fraction isolated from antiserum 0C2 was able to produce a marked reduction in the ability of the synthetic enkephalin [D-Ala2,D-Leu5