Abstract
Spectrophotometric and fluorimetric substrate couple titrations and potentiometric spectrophotometric titrations were used to determine the oxidation-reduction potentials of components showing absorbance or fluorescence at the wavelengths attributable to the flavoproteins of mitochondria fractionated using digitonin together with sonication. A pure mitoplast fraction devoid of cytochrome b5 contamination could be obtained using 230 µg digitonin/mg of mitochondrial protein. The digitonin-soluble fraction contained a species havingE m 7 .4=−123 mV and probably represents the outer membrane flavoproteins. The inner membrane-matrix fraction, treated with ultrasound, provided evidence of a flavoprotein species with low redox potential (E m 7 .4=−302 mV) in the matrix fraction. The −302 mV component is probably lipoamide dehydrogenase. A high redox potential species withE m 7 .4=+19 mV in titrations with the succinate fumarate couple was located in the inner membrane vesicles and is probably identical with succinate dehydrogenase. The electron-transferring flavoprotein (ETF) was isolated from bovine heart mitochondria and itsE m 7 .4=−74 mV determined. The component in the matrix fraction with an apparentE m 7 .4=−56 mV probably represents ETF, and that in the inner membrane fraction with an apparentE m 7 .4=−43 mV the NADH dehydrogenase flavoprotein. A component in an apparently low concentration withE m 7 .4=+30 mV was detected in the inner membrane fraction. This probably represents the ETF-dehydrogenase flavoprotein. The origin of the flavoprotein fluorescence of mitochondria and intact tissues is discussed.
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Voltti, H., Hassinen, I.E. Oxidation-reduction midpoint potentials of mitochondrial flavoproteins and their intramitochondrial localization. J Bioenerg Biomembr 10, 45–58 (1978). https://doi.org/10.1007/BF00743226
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DOI: https://doi.org/10.1007/BF00743226