Quantification of the content of fluorescent flavoproteins in mitochondria from liver, kidney cortex, skeletal muscle, and brain.

The flavoprotein fluorescence emission spectra of mitochondria from rat liver, rat kidney cortex, rat skeletal muscle, and rat brain were compared using free FAD as a standard. On the basis of distinct spectral characteristics and reduction pattern it was possible to differentiate between fluorescence caused by alpha-lipoamide dehydrogenase and electron-transfer flavoprotein. The amount of these flavoproteins in the different mitochondria was quantified and compared with the maximal rates of respiration with the substrates glutamate plus malate and octanoylcarnitine plus malate. It was observed that there is a good correlation between the fractional content of electron-transfer flavoprotein (with respect to alpha-lipoamide dehydrogenase) and the fractional beta-oxidation capacity (with respect to the glutamate plus malate oxidation rate). This method is applicable for the detection of defects of alpha-lipoamide dehydrogenase and electron-transfer flavoprotein in mitochondrial myopathies.