Question

Answer the following questions regarding glycogen phosphorylase.

A biochemical test shows that an individual lacks the muscle form of glycogen phosphorylase.

1. What would be the biochemical consequence of this metabolic defect? (i.e. what pathway is affected and in what way?)
2. What would be the physiological consequence for the person?

Answer 1

i. Glycogen phosphorylase is the first enzyme used in glycogenolysis reaction that is the breaking down of glycogen(n) into glucose 1 phosphate and glycogen (n-1). This glucose-1-phosphate further can take part in glycolysis or in pentose monophosphate pathway by being converted into Glucose-6-phosphate. This Glucose-6-phosphate can also be converted to glucose in liver cell by the enzyme glucose-6-phosphatase. So if the glycogen phosphorylase is absent the metabolic breakdown of glycogen will be hampered.

ii. If the enzyme is absent, the glycogen cant be broken down so there must be the accumultion of glycogen and glycogen storage diseases can be occured. As per the question this enzyme is muscle glycogen phosphorylase so then the bsence of that particular enzyme cause Glycogen Storage Disease IV (GSD V) which is also known as McArdle disease. This disease has phenotypic manifestations like  exercise intolerance with muscle pain, painful cramps, and myoglobin in the urine which is known as Myoglobinuria. The latter may result from the breakdown of skeletal muscle known as rhabdomyolysis, a condition in which muscle cells breakdown, sending their contents into the bloodstream.