Isoleucine hydroxamate, an isoleucine antagonist

Isoleucine hydroxamate (Ile.Hdx) was found to inhibit the growth of Serratia marcescens and to antagonize isoleucine. At a low concentration of Ile.Hdx, at which the growth of the wild strain was completely inhibited, the growth of an isoleucine auxotroph was not inhibited in the medium containing a limiting amount of d-threonine as the isoleucine source. At a higher concentration, this antagonist exhibited a considerable inhibitory effect on the growth of the auxotroph. Ile.Hdx showed the same inhibitory effect as isoleucine on l-threonine dehydratase activity at the concentrations 10 times those of isoleucine. Ile.Hdx caused also derepression of isoleucine-valine biosynthetic enzymes and the derepression was overcome by isoleucine. These results indicate the Ile.Hdx causes growth inhibition by its effects on isoleucine metabolism.