MEDizzy - Consider a 40-year-old man who has just initiated a 24 h

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Nutrition and Vitamins

Consider a 40-year-old man who has just initiated a 24 h fast. Which of the following cofactors are necessary so that his blood glucose levels can be kept constant?

ExplanationBiotin is required for pyruvate carboxylase (the enzyme that converts pyruvate to oxaloacetate), an enzyme necessary for gluconeogenesis from any TCA cycle precursor (and pyruvate). The B6 is required for glycogen phosphorylase (the ability to produce glucose from glycogen) and for transamination reactions, which are necessary for amino acids (such as alanine, aspartic acid, and glutamic acid) to provide carbons for gluconeogenesis. The niacin is required to produce NADH, which is needed to reverse the glyceraldehyde-3-phosphate dehydrogenase step during gluconeogenesis. It is also needed for lactate to be converted to pyruvate, and lactate (provided by the red blood cell) is a major gluconeogenic precursor. The lipid-soluble vitamins (D and K) are not required for glucose production and release (vitamin D is needed for calcium metabolism, and vitamin K is required for the carboxylation of glutamic acid side chains of proteins involved in blood clotting).