Fig. 4. Effect of halothane on guanosine-5′-triphosphate (GTP) hydrolysis rate (GTPase activity) of the α isoform-3 G-protein subunit (Gα^i-3) and the heterotrimer composed of Gα^i-3, and the untagged β isoform-1 (β¹) and amino-terminus hexahistadine-tagged, Flag-tagged γ isoform-2 G-protein subunits (Gα^i-3β¹γ^2HF). Proteins were expressed in and purified from  Spodoptera frugiperda insect cells. GTPase activity was determined using a standard phosphohydrolase assay with radiolabeled [g³²Pi]GTP as described in detail in the Materials and Methods. Assays were performed in the absence (control) or presence of 3 mm halothane. Data are presented as mean ± SE of 9–12 assays. * Significant difference from values measured in the absence of halothane (control).