title: Modulation of the flavin redox potential as mode of regulation of succinate dehydrogenase activity.
abstract: The redox properties of flavin in active and non-active (oxaloacetate reacted) soluble succinate dehydrogenase were studied. Quantitative analysis of reductive activation titrations of redox titrations of active and non-active enzyme reveal that the redox potential of the histidyl-flavin in the active enzyme (-3 +/- 15 mV) is high enough to allow reduction by succinate, whereas in the non active enzyme it is -196 +/- 19 mV, far to low to be reduced by substrate. The flavin radical in the active enzyme attains 60% of total flavin at a poised redox potential of about +60 mV, upon addition of oxaloacetate the magnitude of the signal is diminished and the potential where it reaches maximal concentration is shifted by about -200 mV. A mechanism is proposed which ascribes the fundamental difference between active and non-active enzyme to the inability of the latter to be reduced by substrate.
mesh_terms: D000818:Animals; D002417:Cattle; D004789:Enzyme Activation; D005415:Flavins / Q000378:metabolism*; D005650:Fumarates; D008433:Mathematics; D009206:Myocardium / Q000201:enzymology; D010084:Oxidation-Reduction; D013385:Succinate Dehydrogenase / Q000378:metabolism*; D013386:Succinates
chemical_list: D005415:Flavins; D005650:Fumarates; D013386:Succinates; D013385:Succinate Dehydrogenase