Some Aspects of the Regulation of Amino Acid Biosynthesis in a Branched Pathway

For reasons that have been stated earlier (Stadtman, Cohen, Le Bras and de Robichon-Szulmajster 1961a, 1961b), we have been especially interested in the study of the regulation of the reactions involved in branched biosynthetic pathways. During the past few years, we have been studying the regulation of the biosynthesis of the aspartic acid family of amino acids in Escherichia coli. In this organism, diaminopimelic acid (DAP), lysine, methionine, threonine and isoleucine are products of the branched pathway, illustrated in Fig. 1. The various points at which endproduct inhibition has been observed in this pathway are indicated in this figure. It will be noted that such inhibition occurs at each branch point.