Diagram for citrate metabolism and bicarbonate formation. Shown are key enzymatic reactions catalyzing the formation and degradation of citrate and oxaloacetate, the latter an important metabolite in the TCA (Krebs) cycle, gluconeogenesis as well as the formation of reducing equivalents required for fatty acid biosynthesis. Note that each turn of the TCA cycle generates 2 moles of bicarbonate. The relative flux of oxaloacetate through gluconeogenesis versus the steps catalyzed by MDH and malic enzymes will depend on other metabolic circumstances beyond the scope of this discussion. MDH, malate dehydrogenase; PDH, pyruvate dehydrogenase; acetyl-S-CoA, acetyl-S-coenzyme A.
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