Enzyme Repression in Anabolic Pathways

Abstract

Fifty years ago, the following observation was made at the Pasteur Institute: if the wild-type of E. coli was grown in the presence of an exogenous amino acid, the content of an enzyme involved in the biosynthesis of this amino acid was significantly lower in the cell suspensions or the extracts from these bacteria. Table 1 illustrates this observation in the case of methionine biosynthesis. The experiment has been carried out with a strain constitutive for β-galactosidase, in order to ascertain the specificity of the effect observed. All the amino acids reduce somehow the galactosidase specific activity; there is no correlation between this reduction and the effects on the levels of methionine synthase. Whereas the addition of methionine does not affect β-galactosidase, it has a spectacular effect on methionine synthase levels.