Question

In: Biology

When would serine 32 be phosphorylated, during glycolysis or gluconeogenesis?

When would serine 32 be phosphorylated, during glycolysis or gluconeogenesis?

Solutions

Expert Solution

Answer: Gluconeogenesis

Explanation:

The irreversible steps in gluconeogenesis are

i. Conversion of pyruvate to phosphoenolpyruvate by an enzyme phosphoenol pyruvate carboxylase.

ii. Conversion of fructose 1,6 bisphosphate to fructose 6 phosphate by the enzyme fructose 1, 6 bisphosphatase which has a specific serine-32 residue and requires Magnesium ions to catalyze the reaction.

iii. Conversion of glucose 6 phosphate to glucose by the enzyme glucose 6 phosphatase whose presence or absence determines whether a tissue can contribute glucose to the blood or not. Glucose 6 phosphatase is present abundantly in liver and kidney and absent in muscle, brain and adipose tissue

Glucagon, a peptide hormone secreted from the alpha cells of islets of langerhans of pancreas, stimulates the adenylate cyclase in the liver. This results in synthesis of cyclic AMP which in turn activate protein kinase A. Protein kinase A, then binds (by phosphorylation of ATP) to the Serine 32 residue of the fructose 1,6 bisphosphatase.

The activity of phosphatase is increased with simultaneous decreased activity of phosphofructokinase.

These steps reduces the levels of fructose 2,6 bisphosphate which ultimately inhibits the glycolysis and stimulates gluconeogenesis

Thus, it can be concluded that phosphorylation of serine 32 occurs during gluconeogenesis in response to glucagon and increases the blood glucose levels


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