The dopamine D2 receptor in bovine brain striatum exists in a high- and a low-affinity state for dopamine. The high-affinity state is believed to arise from coupling with a guanine nucleotide-binding protein, to be disrupted by the addition of GTP. We found that antibodies specific to the C-terminal region of the alpha-subunit of Go and Gi cause a shift from high- towards low-affinity, demonstrating that the C-terminus of G alpha is involved in the receptor G protein contact. Purification of the D2 receptor by affinity chromatography via immobilized agonists or antagonists results in the copurification of both Go and Gi proteins. However, this copurification is of a nonspecific nature and prevents the detection of putative specific receptor.G protein complexes.