A rate-limiting enzyme catalyzes the first step in the conversion of a toxic metabolite to a urinary excretion product. Which of the following mechanisms for regulating this enzyme would provide the most protection to the body?

A. The product of the pathway should be an allosteric inhibitor of the rate-limiting enzyme.
B. The product of the pathway should act through gene transcription to decrease synthesis of the enzyme.
C. The toxin should act through gene transcription to increase synthesis of the enzyme.
D. The enzyme should have a high Km for the toxin.
E. The toxin allosterically activates the last enzyme in the pathway.