Reversible dissociation of flavin mononucleotide from the mammalian membrane-bound NADH: ubiquinone oxidoreductase (complex I)

Conditions for the reversible dissociation of flavin mononucleotide (FMN) from the membrane-bound mitochondrial NADH: ubiquinone oxidoreductase ( complex I) are described. The catalytic activities of the enzyme, i.e. rotenone-insensitive NADH: hexaammineruthenium III reductase and rotenone-sensitive NADH: quinone reductase decline when bovine heart submitochondrial particles are incubated with NADH in the presence of rotenone or cyanide at alkaline pH. FMN protects and fully restores the NADH-induced inactivation whereas riboflavin and flavin adenine dinucleotide do not. The data show that the reduction of complex I significantly weakens the binding of FMN to protein thus resulting in its dissociation when the concentration of holoenzyme is comparable with K-d (similar to 10(-8) M at pH 10.0). (C) 2007 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.