An individual with chronic hypoglycemia was suspected of having a defect in one

Question

An individual with chronic hypoglycemia was suspected of having a defect in one of the enzymes unique to gluconeogenesis. To identify the defective enzyme, tissue samples from a normal liver were compared to samples from the patient’s liver biopsy, using a biochemical assay that measures glucose production from glycerol or malate. It was found that incubation with glycerol produced normal amounts of glucose in both the control and biopsied liver samples; however, incubation with malate did not lead to glucose production in the liver biopsy, even though it did lead to glucose production in the control liver sample. On the basis of these observations, which of the 4 main gluconeogenic enzymes is most likely defective in this individual? Explain your reasoning and what data you used to rule out enzymes.

Explanation / Answer

Glycerol entered into glucose production through DHAP (dihydroxyacetone phosphate)formation while malate entered in glucose production through OAA (oxaloacetate) formation.

During Glucose formation from Glycerol, it first converts into DHAP which then either converts into glyceraldehyde-3-phosphate by triose phosphate isomerase or into Fructose-1,6-bisphosphate by aldolase and then subsequently these products are converted into glucose during gluconeogenesis.

malate to glucose production takes place through OAA production by malate dehydrogenase enzyme which then further convert into phosphoenolpyruvate by an enzyme named "PEP carboxylase" which then converted into Glucose by the same sequence of the enzymes that participates into glycolysis pathway.

As in hypoglycemia glucose is quickly metabolized, results in low glucose level, therefore, it suggests that all enzyme participating in glycolysis is working fine. Therefore, enzymes that likely to be defective could be pyruvate carboxylase, PEP carboxylase, malate dehydrogenase and triose phosphate isomerase.

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