Gtp

GTP+iso GTPyS

Wild type

GTP GTP+iso GTPyS Mutant figure above, what do you conclude about the effect of the mutation on Gsa activity in the presence of GTP alone compared with GTP-yS alone or GTP plus isoproterenol (iso)?

b. In the transfected cells described in part a, what would you predict would be the cAMP levels in cells transfected with the wild-type Gsa and the mutant Gsa? What effect might this have on the cells?

c. To further characterize the molecular defect caused by this mutation, the intrinsic GTPase activity present in both wildtype and mutant Gsa was assayed. Assays for GTPase activity showed that the mutation reduced the Kcat_GTP (catalysis rate constant for GTP hydrolysis) from a wild-type value of 4.1 min-1 to the mutant value of 0.1 min-1. What do you conclude about the effect of the mutation on the GTPase activity present in the mutant Gsa subunit? How do these GTPase results explain the adenylyl cyclase results shown in part a?

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