Why is the hydrolysis of GTP by a G-protein essentially irreversible?
A) GDP immediately hydrolyzes to GMP and Pi
B) GDP is metabolized to cGMP
C) GDP remains bound after Pi is liberated
D) GTP cannot be synthesized from GDP
E) The Km for Pi is too low

Question

Quizplus · Accepted Answer

In G-protein signaling, when GTP is hydrolyzed to GDP, the GDP molecule remains bound to the G-protein, while the inorganic phosphate (Pi) is released. This is referred to as "tight binding" and results in a conformational change that makes it difficult for the GDP to be released from the G-protein. This tight binding essentially makes the hydrolysis of GTP irreversible, as it prevents reformation of a GTP-bound state. Therefore, choice C is the best answer, as it describes the specific mechanism responsible for the irreversible nature of GTP hydrolysis by a G-protein.

Why Is the Hydrolysis of GTP by a G-Protein Essentially