AN ELECTRON-TRANSPORT SYSTEM ASSOCIATED WITH THE OUTER MEMBRANE OF LIVER MITOCHONDRIA

This paper reports a study of the "external" NADH-cytochrome c reductase system of rat-llver mitochondria

Gian Luigi Sottocasa; Bo Kuylenstierna; Lars Ernster; Anders Bergstrand

2004

Scholarcy highlights

  • It is has been observed, first in 1951 by Lehninger and by several investigators since, that preparations of rat-liver mitochondria catalyze a rapid oxidation of exogenous NADH in the presence of added cytochrome c
  • The oxidation of intramitochondrial NADH, generated here by ~-hydroxybutyrate as added substrate, was greatly stimulated by ADP, indicative of tightly coupled phosphorylation; it was unaffected by added cytochrome c; and it was completely inhibited by rotenone and antimycin A
  • The data reported in this paper seem to leave little doubt that the so called "external" N A D H cytochrome c reductase system found in preparations of liver mitochondria is a true mitochondrial constituent and cannot be explained on the basis of microsomal contamination
  • The mitochondrial preparations exhibited only marginal activities of glucose-6-phosphatase and of other exclusively microsomal enzymes, and their rotenone-insensitire NADH~:ytochrome c reductase activity was almost l0 times higher, in relation to these activities, than the corresponding ratios found with liver microsomes
  • If the extent of microsomal contamination of the mitochondrial preparations were as high as indicated by the rotenone-insensitive NADH~:ytochrome c reductase activity or the cytochromal b5 content - 37 or 27% of the total protein--it should be possible to separate the two elements by continuous density gradient centrifugation, in view of the
  • Our results strongly suggest that the rotenoneinsensitive NADH-cytochrome c reductase system present in liver mitochondria is associated with the outer mitochondrial membrane
  • With the combined swelling-shrinking and sonication procedure, which resulted in the quantitatively best separation of the inner and outer membranes, about 58 % of the total protein was recovered in the heavy subfraction, 9% in the light subfraction, and 33% in the soluble subfraction

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