Gluconeogenesis

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Gluconeogenesis
R. C. Gupta Professor and Head Department of
Biochemistry National Institute of Medical
Sciences Jaipur, India
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Gluconeogenesis is synthesis of glucose from
non-carbohydrate substrates
Gluconeogenesis occurs when the availability of
carbohydrates is low
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The main substrates for gluconeogenesis are

• Lactate
• Glycerol
• Amino acids (except leucine lysine)
• Intermediates of glycolysis
• Intermediates of citric acid cycle

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Energy barriers
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Bypassing the energy barriers
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Pyruvate enters mitochondria and is converted
into oxaloacetate by pyruvate carboxylase
Oxaloacetate comes out of mitochondria with
the help of malate shuttle
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It is converted into phosphoenol pyruvate by
phosphoenol pyruvate carboxykinase
The phosphate group is provided by GTP
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Cori cycle
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Glucose-alanine cycle
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Alanine transfers its amino group to
a-keto-glutarate in liver
Alanine is converted into pyruvate, and
a-keto-glutarate into glutamate
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Amino group of glutamate is used to synthesize
urea
Pyruvate is converted into glucose by
gluco-neogenesis which goes back to liver via
blood
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Regulation
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Fructose-2,6-biphosphate is the allosteric
modifier of two enzymes
It activates phosphofructokinase-1 which
increases glycolysis
It inhibits fructose-1,6-biphosphatase which
decreases gluconeogenesis
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Fructose-2,6-biphosphate is formed from
fructose-6-phosphate
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