G-Protein Coupled Receptors sense extracellular signals and activate different Guanine nucleotide binding proteins. Upon activation, the alpha subunit of the G protein (GNAS) can directly bind to SRC. In the presence of active GNAS, SRC can autophosphorylate the 419-tyrosine residue, which leads to the subsequent activation of SRC. Physiologically, the SRC family have implications in cell growth and cancer. GNAS increases SRC enzymatic activity by decreasing Km and not affecting Vm.