Chapter 19.7, Problem 19.15P

1. (a) L-Threonine is converted to L-isoleucine in a linear pathway involving five separate enzymes. Which of the enzymes in the following pathway is most likely inhibited by the product of the pathway, L-isoleucine?

   L-threonine $\stackrel{\text{E1}}{\to }\text{A}\stackrel{\text{E2}}{\to }\text{B}\stackrel{\text{E3}}{\to }\text{C}\stackrel{\text{E4}}{\to }\text{D}\stackrel{\text{E5}}{\to }$L-isoleucine

2. (b) If product A inhibited the first enzyme in the pathway (E1), could this be called feedback control? Explain.