Feedfoward inhibition in biosynthetic pathways: inhibition of the aminoacyl-tRNA synthetase by intermediates of the pathway.

The stability of an amino acid biosynthetic pathway controlled by end-product inhibition is significantly improved if, in addition, the corresponding aminoacyl-tRNA synthetase is inhibited by an intermediate in the pathway. The more proximal the feedforward modifier is to the initial substrate, the more stable is the system. The temporal responsiveness of a system having both feedback and feedforward inhibition also is improved by having the feedforward modifier located at the beginning of the pathway. According to all other criteria that have been used previously to determine the functional effectiveness of biosynthetic pathways, the behavior of such a system essentially is unaffected by the position of the feedforward modifier in the pathway.