A 2-year-old boy with weakness on exertion is found to have a pyruvate carboxylase deficiency. Which of the following compounds could this child use as a substrate for gluconeogenesis?

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Glycerol can be used as a substrate for gluconeogenesis because it enters the pathway downstream of the pyruvate carboxylase step, which is deficient in this child. A deficiency in pyruvate carboxylase would restrict the use of carbons from pyruvate, alanine, and lactate for glucose synthesis via gluconeogenesis. Therefore, the burden is shifted to the use of the glycerol backbone of stored triglycerides. Glycerol is phosphorylated within hepatocytes to glycerol 3-phosphate and then converted to DHAP via the action of glycerol-3-phosphate dehydrogenase. The DHAP then can be used for glucose production via gluconeogenesis.

A 2-Year-Old Boy with Weakness on Exertion Is Found to Have