Glutathione-dependent conversion of N-ethylmaleimide to the maleamic acid by Escherichia coli: an intracellular detoxification process

The electrophile N-ethylmaleimide (NEM) elicits rapid K+ efflux from Escher ichia coli cells consequent upon reaction with cytoplasmic glutathione to f orm an adduct, N-ethylsuccinimido-S-glutathione (ESG) that is a strong acti vator of the KefB and KefC glutathione-gated K+ efflux systems. The fate of the ESG has not previously been investigated. In this report we demonstrat e that NEM and N-phenylmaleimide (NPM) are rapidly detoxified by E. coli. T he detoxification occurs through the formation of the glutathione adduct of NEM or NPM, followed by the hydrolysis of the imide bond after which N-sub stituted maleamic acids are released. N-Ethylmaleamic acid is not toxic to E. coli cells even at high concentrations. The glutathione adducts are not released from cells, and this allows glutathione to be recycled in the cyto plasm. The detoxification is independent of new protein synthesis and NAD()-dependent dehydrogenase activity and entirely dependent upon glutathione. The time course of the detoxification of low concentrations of NEM paralle ls the transient activation of the KefB and KefC glutathione-gated K+ efflu x systems.