Mechanistic studies on CDP-6-deoxy-delta(super 3,4)-glucoseen reductase: the role of cysteine residues in catalysis as probed by chemical modification and site-directed mutagenesis

The inactivation of the flavoenzyme, CDP-6-deoxy-delta(super 3,4)-glucoseen reductase (E3) possessing one ferredoxin type (2Fe-2S) cluster, with 5,5'-dithiobis(2-nitrobenzoic acid) and N-ethylmaleimide is a pseudo first order reaction. Except the cysteine residues, the flavin and (Fe2-2S) cluster suffer no modification. Stabilization of the charge transfer complex between E3 and NADH is possible by Cys-296. The Cys-75 restricts the proper adjoining of the redox centers, causing reduced electron transfer and results in enzyme inactivation.