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Evidence for the localization of the mitochondrial glycerol-phosphate dehydrogenase in the outer phase of the inner membrane is presented.

  • 1
    Glycerol-phosphate does not permeate through the inner membrane to the matrix space in a number of mitochondria which actively oxidize glycerol-phosphate.
  • 2
    The impermeability of the inner membrane to ferricyanide is demonstrated and this forms a basis for elucidating membrane localization of carriers.
  • 3
    In mitochondria from various tissues ferricyanide can interact directly with glycerolphosphate dehydrogenase but not with succinate dehydrogenase.
  • 4
    The oxidation of glycerol-phosphate, in contrast to that of succinate, is insensitive to substrate depletion brought about by uncouplers.
  • 5
    The results are interpreted to show that both the substrate and the acceptor-site of glycerol-phosphate dehydrogenase are exposed to the outer side of the inner membrane. Thus, for the operation of the glycerol-phosphate dehydrogenase, mitochondria do not require translocases for glycerol-phosphate and dihydroxyacetone-phosphate.