An enzyme fraction which catalyzes the reduction of N-ethylmaleimide (NEM) to N-ethylsuccinimide in the presence of reduced nicotinamide adenine dinucleotide phosphate was partially purified from Escherichia coli extracts. The apparent Michaelis-Menten constant for NEM was estimated to be 4μM. The enzyme showed a rather broad pH optimum between 7 and 8. The enzyme was 90% inhibited after being heated at 55° for 15 min, and was 94% inhibited by 1 mM p-hydroxymercuribenzoic acid.
