The Effects of Hexanol on Gα_i Subunits of Heterotrimeric G Proteins

Alcohols and other anesthetics interfere with the function of a variety of systems regulated by guanosine triphosphate (GTP)-binding proteins (G proteins). We examined the effect of hexanol on the activity of the a subunit (Gα_i1) of heterotrimeric G proteins. The GTP hydrolysis activity of recombinant Gα_i1 was 0.029 mole Pi · mole Gα_i1^-1 · min^-1 and was inhibited by hexanol at concentrations larger than 10 mM, with a 50% inhibitory concentration of 22 mM. Circular dichroism spectroscopy revealed that hexanol decreased the denaturation temperature of Gα_i1 from 47.2°C to 42.5°C without altering its secondary structure at 10°C. Hexanol (30 mM) reduced the amount of monomeric Gα_i1 in solution measured by size-exclusion chromatography, indicating that hexanol caused protein aggregation. However, the rate of GTPγS binding to Gα_i immunoprecipitated from airway smooth muscle membranes was not affected by 30 mM hexanol. Excluding the apparent inhibition of recombinant Gα _i1 resulting from aggregation-induced artifact, we found no evidence that the hexanol-induced inhibition of receptor-activated Gα _i-coupled pathways in intact airway smooth muscle resulted from direct inhibition of the intrinsic rate of [³⁵S]GTPγS binding to Gα_i.