Bioprocess Engineering 2nd Edition by Fikret Kargi,Michael Shuler

Exercise 10

Consider the aspartic acid pathway shown in Fig. 4A.1. Assume you have been asked to de-
velop a high-lysine-producing mutant. What strategy would you pursue? (That is, which steps
would you modify by removing feedback inhibition, and what changes in medium composi-
tion would you make over a simple mineral salts-glucose base medium?) Figure 4A.1 A simplified diagram of the aspartate pathway in E. coli. Each solid arrow
designates a reaction catalyzed by one enzyme. The biosynthetic products of the pathway
(in boldface) are all allosteric inhibitors of one or more reactions. Careful study of this diagram reveals that with a single exception (the inhibition exerted by valine) the inhibition
imposed by one amino acid does not cause starvation for a different amino acid. Part (a)shows the regulatory interrelationships of the L-lysine, L-methionine, and L-isoleucine
branches of the pathway. Part (b) shows the regulatory interrelationships of the
L-isoleucine, L-valine, and L-leucine branches