Studies on Succinate Dehydrogenase

Succinate dehydrogenase. XVIII. Regulation of succinate dehydrogenase activity by reduced coenzyme Q10

“…Kearney (1957) has reported an energy of activation of 36 kcal/ mole for the activation of succinate dehydrogenase by succinate. The value for the deactivation process has never been determined, since the removal of bound substrate or competitive inhibitor is a time-consuming process, which precludes accurate measurement of the rate of the deactivation (Kimura et al, 1967). Activation by NADH, on the other hand, permits rate studies of the deactivation process because one may rapidly oxidize all remaining NADH and CoQi0H2 by nonenzymatic reaction with PMS, whereupon spontaneous deactivation occurs.…”

“…Dependence of the Rates of Forward and Reversed Electron Transport on the Activation of Succinate Dehydrogenase. There is an abundance of evidence for the importance of activation in overall succinoxidase activity in various particulate preparations, including intact mitochondria (Kearney, 1957;Thorn, 1962;Kimura et al, 1967). Thus far, however, no studies have been reported of the quantitative relations between the degree of activation of succinate dehydrogenase and the rate of electron flux in the respiratory chain, including energy-dependent reactions, in other words the extent of activation required before the dehydrogenase ceases to be rate limiting.…”

“…The activation has been observed in intact mitochondria, membrane preparations, and the soluble, purified enzyme from a variety of mammalian sources and aerobic yeast cells (Kearney, 1957;Thorn. 1962;Singer et al, 1966) and was found to be reversible upon removal of the activator (Kimura et al, 1967). Two characteristics of the activation process are noteworthy; the high energy of activation (36 kcal/mole), suggestive of a protein modification (Kearney, 1957), and the fact that activation affects only certain activities of the enzyme (the reduction of PMS,1 ferricyanide, and of the respiratory chain by succinate, which are thought to involve nonheme iron), but does not alter the fumarate reductase activity (which is thought to involve only the FAD moiety of the enzyme) (Kearney, 1957; Kimura etal., 1967).…”

The effect of opposing effectors on activation level of succinate dehydrogenase: equilibrium and kinetic studies

“…Beef heart mitochondria and ETP were made according to Ringler et al (1963); ETPh was made by the method of Hansen and Smith (1964). Succinate dehydrogenase activity was measured spectrophotometrically using the DCPIP-PMS method (Kimura et al, 1967) as modified by Gutman et al (1971a). In order to avoid activation in situ, the assay was carried at 13-15 °C.…”

“…To account for possible inactivation, control samples were activated in the cuvette (containing 20 mM succinate, 60 mM KPO4 buffer, pH 7.6, and 2 mM KCN) for 15 min at 30 °C and cooled to the assay temperature, (15 °C), and the reaction was started by addition of DCPIP and PMS (Kimura et al, 1967). This procedure allows estimation of the extent of competitive inhibition by oxaloacetate which has been carried over.…”