The activities of pyruvate dehydrogenase and oxo-glutarate dehydrogenase can be reliably measured by coupling the production of NADH to the reduction of added cytochrome c. Maximum activities required the addition of NADH-cytochrome c reductase activity prepared from rat heart mitochondria. Compared to other spectrophotometric assays this method provides an eight-fold increase in sensitivity and is particularly suitable for use with small tissue samples such as needle-biopsy samples of human skeletal muscle. Measurements of activities in rat tissues showed them to be in the order skeletal muscle < liver < heart ≤ brown adipose tissue. Activities in normal human skeletal muscle were similar to those of rat muscle, tn the rat tissues specific differences were seen in the relative activities of the two complexes and cytochrome c oxidase suggesting tissue-specific differences in the activities of the dehydrogenases and components of the electron-transport chain.

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