ИСТИНА

Two ferricyanide reactive sites in soluble reconstitutively active succinate dehydrogenase are described. Site 1 has a Km value of 3x10-3 for ferricyanide and the Vmax for its activity is about 25% of that with PMS. Site 2 has a Km value of 2.5- 10-4 M for ferricyanide and the Vmax for its activity is equal to that of succinate-PMS reductase. Only site 1 is reactive towards ferrlcyanide in particulate preparations of the enzyme (succinate: cytochrome c reductase; Keilin-Hartree heart muscle preparation). The activlty of site 2 is much more labile than succinate-PMS reductase activity. Exposure of the enzyme at 0° in air for 2 hours inactivates 80% of site 2. High concentrations of ferricyanlde (1-3 mM) rapidly destroy site 2. Treatment of the enzyme with p-CMB (30 nmoles/mg), followed by removal of the inhibitor, completely inactivates site 2 without any effect on site 1 or succinate-PMS reductase activity. The data obtained are consistent with the existence of two active redox centers in succlnate dehydrogenase in submitochondrial particles. Site 2 is presumed to be responsible for electron transfer between dehydrogenase and the respiratory chain, being non-accesslble to ferricyanide in the particulate preparations but highly reactive in the soluble, reconstitutively active enzyme; site I is readily accessible to ferricyanide, being slowly reactive in both particulate and soluble, reconstitutivety active or inactive states.