Question

You are conducting an experiment to study epinephrine signaling. You replaced GTP with a poorly hydrolysable GTP analog (the analog is a compound with a similar structure to GTP that cannot be hydrolyzed to GDP). Which of the following results do you expect:  Indicate A or B

A.Loss of epinephrine signaling?

B. Maintenance or continuation of signaling even in the absence of epinephrine?

Which of the following would REVERSE the maintenance or continuation of signaling even in the absence of epinephrine. Indicate A or B

A. Activating Adenylate Cyclase function

B. Inhibiting Adenylate Cyclase function

Answer 1

Q1. Maintenance or continuation of signaling even in the absence of epinephrine.

If GTP is non-hydrolysable, then the alpha subunit of G-protein remains always GTP bound, and thus always active. The GTP will not easily hydrolyse to give the inactive form of alpha-GDP. Such a constitutively active alpha subunit will continue the signaling process even in the absence of epinephrine.

Q2. Inhibiting adenylate cyclase function.

Continuation of signaling can be reversed if a downstream component is prevented from functioning. Adenylate cyclase is such a downstream enzyme that transmits the signal forward. If its activity can be inhibited, then even constitutively active alpha subunit cannot maintain the signal in absence of epinephrine.