An investigator has a purified sample of muscle phosphorylase b that is known to

Question

An investigator has a purified sample of muscle phosphorylase b that is known to be relatively inactive.

a) Suggest two different methods that she could use to activate the enzyme. b) Once she has activated the enzyme she sets up a reaction containing (ONLY!) the following components: 25 uL of a stock solution of unbranched glycogen, 3.00 mL of 0.1 M HEPES buffer, pH 7.5, 25 uL of a 100 uM stock solution of GTP. She is surprised to see NO activity in her assay when she adds a small amount of enzyme. Explain to her what she did wrong and suggest a solution to her problem.

Explanation / Answer

Based on the given data,

Glycogen phosphorylase is an enzyme that is involved in the removal of individual glucose unit from glycogen in the form of glucose-1-phosphate. Phosphorylation is an important process for enhancing the activity of the enzyme glycogen phosphorylase. A dephosphorylation reaction reduces the activity of the enzyme turning it to the less active form.

The reaction catalyzed by the enzyme is as follows:

(-1,4 glycogen chain)n + Pi ? (-1,4 glycogen chain)n-1 + -D-glucose-1-phosphate

a)

The enzyme Glycogen phosphorylase can activate by two strategies:

b)

The given components for the reaction are as follows:

However, the enzyme cannot convert the substrate into product. The Inorganic phosphate is also required for the conversion of glycosyl residues in glycogen to glucose 1-phosphate.

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