Guanine nucleotide-binding proteins (G proteins) are involved as a modulator or transducer in various transmembrane signaling systems. The beta and gamma chains are required for the GTPase activity, for replacement of GDP by GTP, and for G protein-effector interaction. G proteins are composed of 3 units, alpha, beta and gamma. Retinal rod outer segment. Belongs to the G protein gamma family. In PubMed:3917402 the authors propose that Cys-36 and Cys-37 are disulfide bonded because they could not be observed during peptide sequencing, but were observed after reduction by dithiothreitol and reaction with labeled iodoacetamide. The crystallographic structures do not support these cysteines being disulfide bonded. Artifactual oxidation and some other cysteine modifications might be consistent with these observations.