Transport of molecules across mitochondrial membrane

Lesson 31 : Biochemical energetics and biological oxidation

Transport of molecules across mitochondrial membrane

  1. Inner mitochondrial membrane is impermeable to NADH and NAD+.
  2. Must use a shuttle to regenerate NAD+ for glycolysis; solution is to shuttle electrons across membrane, rather than NADH itself.
  3. There are two shuttles in operation:
  1. Glycerol phosphate shuttle

    • Found in insect flight muscles and mammalian cells in which high rates of oxidative phosphorylation must occur
    • Cytosolic glycerol 3-phosphate dehydrogenase converts DHAP to glycerol 3-phosphate
    • Converted back to DHAP by membrane-bound glycerol 3-phosphate dehydrogenase
    • Result is transfer to 2e- to FAD --> Q ---> complex III
    • Produces fewer ATP molecules (1.5 vs. 2) because complex I is bypassed

  2. Malate-aspartate shuttle

    • Found in liver and heart
    • Cytosolic NADH reduces oxaloacetate --> malate --> transported via dicarboxylate translocase into matrix
    • In matrix, malate --> oxaloacetate --> aspartate ---> transported out via glutamate-aspartate translocase
    • Converted back to oxaloacetate.......
    • No reduction in ATP yield
Last modified: Wednesday, 25 January 2012, 9:47 AM