Abstract
Lactate and alanine are the major precursors of glucose formed in liver by gluconeogenesis. However, incorporation of 14C, when those precursors are labeled with 14C, cannot be used to quantitate rates of gluconeogenesis. That is because an intermediate in the formation of the glucose is oxaloacetate, i.e. alanine and lactate → pyruvate → oxaloacetate → glucose, and oxaloacetate is also an intermediate in the tricarboxylic acid cycle(Figure 1). Consequently, labeled carbon in oxaloacetate, formed from the labeled precursors, exchanges with unlabeled carbon in oxaloacetate formed in the cycle from acetyl-CoA.
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Landau, B.R. (1993). Estimating Gluconeogenic Rates in NIDDM. In: Östenson, C.G., Efendić, S., Vranic, M. (eds) New Concepts in the Pathogenesis of NIDDM. Advances in Experimental Medicine and Biology, vol 334. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-2910-1_15
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