Microcin 15m from Escherichia coli: mechanism of antibiotic action.

It has been previously established that a high proportion of enterobacteria isolated from the intestinal content of humans, mostly Escherichia coli strains, secrete into the culture media antibiotic substances of low molecular weight, which have been called microcins. It was also found that the synthesis of these antibiotics is determined by plasmids. In this paper, a method for the purification of microcin 15m is described, and experimental data are given on the mechanism of its action. The data indicate that this action is based mainly on the inhibition of the first enzyme of the methionine biosynthetic pathway, homoserine-O-transsuccinylase, a similar way to the allosteric inhibition caused by this amino acid.