Theoretical study of formate, tartrate, tartronate, and glycolate production from 6-carbon trioxylate intermediate in the citric acid cycle.

Reaction pathways of side products (formate, glycolate, and tartronate) from dihydroxyfumarate (DHF) were theoretically investigated as DHF is an intermediate in the process of producing tartrates and oxalate from glyoxylate of the citric acid cycle. The proposed pathways for each reaction were mapped by density functional theory (DFT) calculations. The transitions states were confirmed by analyzing the vibrational frequency and the intrinsic reaction coordinate (IRC) theory. The corresponding reaction activation energy, enthalpy change, Gibb's free energy change, and rate of reactions were calculated to get a clear picture of the whole reaction pathway. In the whole process, the decarboxylation reaction showed the highest energy barrier of 20-23 kcal/mol. Proton transfer and hydroxylation reactions were almost barrierless. As most of these reactions have very low energy barrier, our findings elucidate the high probability of those reactions under experimental conditions.