| Conversion of fructose and galactose to glucose
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As discussed in detail in Chapter 24, fructose is metabolized almost exclusively in the liver. It enters glycolysis at the level of triose phosphates, bypassing the regulatory enzyme, PFK-1, so that large amounts of pyruvate may be forced on the mitochondrion for use in energy metabolism or fat biosynthesis. During a gluconeogenic state, this fructose may also proceed toward Glc-6-P, providing a convenient source of blood glucose . Gluconeogenesis from galactose is equally efficient, since Glc-1-P, derived from galactose 1-phosphate (Chapter 25), is readily isomerized to Glc-6-P by phosphoglucomutase. Fructose and galactose are good sources of glucose, independent of glycogenolysis and gluconeogenesis.
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