Question

You’re studying cellular signaling through G-Protein Coupled Receptors (GPCRs). Specifically you’re working on a pair of newly identified GPCRs, GPCR-A and GPCR-B. Each binds the same small ligand, but activates different heterotrimeric G-proteins that act on adenylate cyclase.

• Observe and interpret TABLE 1 described below.
• Assume your experimental Reaction Mixture 1 contain GPCR-A and GPCR-B. You assayed for the levels of cAMP. Your data showed total concentration of cAMP in that reaction mixture was 1000 picomoles per unit protein concentration. You could not conclude which type of GPCR is or are present. In order to identify the type of GPCR present in the mixture, you separated GPCR-A and GPCR-B by column chromatography and purified them. You again assayed for the levels of cAMP in these two reaction mixture. Your data showed Reaction Mixture 2 contains 100 picomoles of cAMP per unit protein concentration, and Reaction Mixture 3 contains 900 picomoles of cAMP per unit protein concentration.

Reaction Mixture	cAMP concentration (pmoles per unit protein concentration)	Predict the type of G protein involved
Reaction Mixture 1: GPCR-A + GPCR-B	1000
Reaction Mixture 2: GPCR-A	100
Reaction Mixture 3: GPCR-B	900

Answer 1