A sample of liver tissue was from a deceased patient genetically deficient in ON

Question

A sample of liver tissue was from a deceased patient genetically deficient in ONE of the enzymes of carbohydrate metabolism. The liver sample had the following characteristics. 1) Homogenates degraded glycogen to glucose-6-phosphate. 2) Homogenates did not synthesize glycogen from any sugar and could not utilize galactose as a carbon source for energy. 3) Glucose 6-phosphate was obtained from lactate, as was galactose. Provide a single enzyme deficiency that could explain the results. You must justify your answer. When growing on lactose, how much energy in the form of ATP could be obtained assuming the malate-aspartate shuttle system was employed?

enzyme answer Is not glycogen synthase

Explanation / Answer

In glycogenolysis three enzymes are there:-

First one is glycogen phosphorylase which breaks down alpha1-4 bonds between adjacent glucose residues of glycogen. So, glycogen breaks down into glucose 1 phosphate.

Second, is glycogen debranching enzyme which is essential for the next step.

Third is glucose 1-phosphate is converted to glucose 6-phosphate via the enzymes phosphoglucomutase.

pt. 1) says that glycogen had been degraded to glucose 6-phosphate, means these three enzymes are there in the homogenate. So, there is no problem with glycogenolysis.

There is a deficiency of glucose 6-phosphatase. This dis allows the conversion of glucose6-phosphate to glucose. When glucose is not there, then glucose 6-phosphate is obtained from lactate (pt. 3)

Pt.2) also says that glycogen is not synthesised from any sugar.

This enzyme deficiency results in the disease:- Glycogen storage disease Type I (GSD I) or von Gierke disease.

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