SUCCINATE-CYTOCHROME-C REDUCTASE - ASSESSMENT OF ITS VALUE IN THE INVESTIGATION OF DEFECTS OF THE RESPIRATORY-CHAIN

Defects of the respiratory chain are important causes of human disease and one of the most commonly used assays in the investigation of thes e patients is the measurement of succinate-cytochrome c reductase. How ever, this assay measures several components of the respiratory chain and the ability to detect a partial defect in one enzyme complex will depend on the amount of control exerted by that enzyme step on overall electron flux. We show that measurement of succinate-cytochrome c red uctase activity may fail to detect partial defects of complex III and therefore is of limited diagnostic value in the identification of comp lex III defects. However, complex II is a major point of control of fl ux through succinate-cytochrome reductase and it is likely that measur ement of the latter will detect defects of complex II.