N-ethylmaleimide as oxidizing agent in biological and non-biological systems

The hypothesis that N-ethylmaleimide (NEM) may function as an oxidizing agent in biological and non-biological systems, has been tested. Spectrophotometric determination of cytochrome a-redox-state have revealed that NEM promotes the transition of this respiratory chain component in a more oxidated state. To overcome the possibility that the NEM effect may be determined by the inhibition on primary dehydrogenase, duroquinol (QH2) has been used as substrate in the presence of rotenone and malonate. The stimulation of cytochrome a-oxidation is correlated to the one on the QH2 oxidation determined by following the formation of duroquinone. In the absence of any biological system, spontaneous oxidation of ferrocyanide and TMPD is greatly increased by NEM. The differential stimulation induced by maleimide and succinimide indicate that the oxidizing effect of NEM may be considered a chemico-physical property of its molecule mainly due to the presence of a double bond. It is proposed that besides a sulfhydryl reagent, NEM behaves as an oxidizing agent with an interacting site in the region QH2-cytochrome a of the respiratory chain.