A-Glycerophosphate shuttle

Shuttle pathways for the transport of electrons across the inner mitochondrial membrane. A. Glycerophosphate shuttle. B. Malate-aspartate shuttle. 

In addition to NADH dehydrogenase, succinic dehydrogenase and other flavopro-teins in the inner mitochondrial membrane also pass electrons to CoQ (see Fig. 21.5). Succinate dehydrogenase is part of the TCA cycle. ETF-CoQ oxidore-ductase accepts electrons from ETF (electron transferring flavoprotein), which acquires them from fatty acid oxidation and other pathways. Both of these flavo-proteins have Fe-S centers. a-Glycerophosphate dehydrogenase is a flavoprotein that is part of a shuttle for reoxidizing cytosolic NADH. 

Dihydroxyacetone (No. 1716) is classified chemically as a ketotriose. It is endogenous in animals and is readily phosphorylated in vivo to form dihydroxyacetone phosphate. Dihydroxyacetone phosphate is involved in several common metabolic pathways, glycolysis and gluconeogenesis, and the glycerophosphate shuttle (Michal, 1999). It is also part of the Calvin cycle in plant metabolism (Michal, 1999). 

The glycerophosphate shuttle is important in muscle in which there is a very high rate of glycolysis (especially insect flight muscle) the malate-aspartate shuttle is especially important in heart and liver. 

Fig. 15.3 The mitochondrial malate and aspartate translocases ( shuttles ) for pyruvate transfer across the mitochondrial membrane, and the a-glycerophosphate translocase.

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