Evidence for oligomeric forms of transducins alpha subunit: formation of intermolecular alpha-alpha disulfide linkages

Transducin, the retinal G-protein, is a heterotrimeric protein composed of alpha, beta and gamma subunits. Intermolecular disulfide linkages between the alpha-subunits of transducin molecules are spontaneously formed when the purified G-protein is placed in a non-reducing buffer system. The beta and gamma subunits do not participate in the intermolecular disulfide bridge formation. The alpha-alpha subunit disulfide bonds result in the inhibition of transducin activation by bleached rhodopsin which is restored by reducing the disulfides with dithiothreitol. The trapping of oligomers by disulfide bond formation provides physical evidence for specific intermolecular interactions between alpha-subunits of transducin.