A patient presents with chronically low blood glucose. Liver biopsy samples are

Question

A patient presents with chronically low blood glucose. Liver biopsy samples are used in two experiments and compared with samples from a normal liver. In the first experiment, the liver tissue samples were incubated with glycerol, and normal glucose production was observed in both the control sample and the patient's sample. (Glycerol can be metabolized to form dihydroxyacetone phosphate.) In the second experiment the liver tissue samples were incubated with malate. The glucose produced by the patient's sample was drastically reduced, but the control sample produced the expected amount of glucose. (Malate can be metabolized to form oxaloacetic acid.) Based on these data, which enzyme is most likely to be defective in the patient?

Explanation / Answer

Option 2nd that is PEP carboxykinase is the correct answer. Malate is converted into oxaloacetic acid which is converted into PEP by PEP carboxykinase. The PEP is converted into glucose by cytosolic gluconeogenic enzymes. Defective in PEP carboxykinase does not convert oxaloacetic acid into PEP and low level of PEP results in low level of glucose.

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