Activation of the succinic dehydrogenase-cytochrome system

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Abstract
The succinic dehydrogenase-cytochrome system of heart-muscle prepns. containing very little inorganic phosphate can be activated by: phosphate, histidine, lysine, aspartic acid, denatured and native globin, glyoxaline-4,5-dicarboxylic acid, ethylenediaminetetraacetic acid, 8-hydroxy-quinoline, pyrophosphate. and tricalcium phosphate gel. KCN also activated the cytochrome c reductase system of heart-muscle prepns. in the absence of phosphate. These same substances were effective in activating oxidation of dihydro-cozymase by heart-muscle prepns. in the absence of phosphate, in reactivating vacuum-dried prepns., in activating low-phosphate kidney prepns., and, to some extent, in activating low-phosphate pigeon breast-muscle prepns. Low-phosphate prepns. which have been activated by 1 of these substances are indistinguishable from the Keilin and Hartree prepn., in phosphate, with 2 exceptions: fluoride does not affect prepns. in the absence of phosphate; low-phosphate prepns. are inactive only after dilution. The activating substances appear to affect the series of electron transport reactions between the factor and cytochromes b and c, or between the factor and diaphorase. This effect is discussed in terms of the mutual accessibility of these components. Heart-muscle succinic oxidase prepns. can oxidize succinate in the absence of inorganic phosphate.