Question

Enzyme $X$ catalyses hydrolysis of $GTP$ into $GDP$. The $GTP$-bound form of $X$ transmits a signal that leads to cell proliferation. The $GDP$-bound form does not transmit any such signal. Mutations in $X$ are found in many cancers. Which of the following alterations of $X$ are most likely to contribute to cancer?

• A. Mutations that increase the affinity of X for GDP
• B. Mutations that decrease the affinity of X for GTP
• C. Mutations that decrease the rate of GTP hydrolysis
• D. Mutations that prevent expression of enzyme X

Answer 1

Answer: (C)

GTP-X complex $\rightarrow$ Active cell division
GDP-X-complex $\rightarrow$ No cell division
and GTP $\ce{ ->[{\text{hydrolysis}}][{\text{X-enzyme}}] GDP}$
Mutation causes the decrease of rate of hydrolysis of GTP. Thus, GTP-X complex remains present for long time and cell division becomes uncontrolled.