Reoxidation Of Nadh And Reduction Of Nadph

NADH is generated in the first two reactions of alcohol metabolism as outlined above. It is necessary for NADH to then be reoxidised to NAD+ so that it can be involved in further oxidation reactions in the cytosol:

The cytosolic NADH is reoxidised by the mitochondrial electron transport system, so substrate shuttles need to be used to transport the H atoms to the mitochondria.

Under some conditions, the rate of transfer of H atoms by these shuttles is less than the rate of NADH generation, so that the concentration of NAD + becomes greatly reduced. This low concentration of NAD + also restricts the conversion of lactate to pyruvate in the liver. This is one element by which alcohol increases the concentration of lactate in the blood.

The low NAD+ level limits the rate of ethanol oxidation by alcohol dehydrogenase (the first step in alcohol metabolism). Alcohol decreases the ratio of NAD + to NADH within the hepatocyte while it is being oxidised.

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