Abstract
Glyoxylate cycle in fatty acid catabolism enhances net production of oxaloacetate, a substrate for gluconeogenesis, in certain bacteria, invertebrates and oilseed in the growth stage. A theoretical model was developed to calculate ATP amount produced in each step of the catabolic pathway, taking into account the fatty acid’s hydrocarbon chain size. Results showed a decrease in energy efficiency in glyoxylate cycle when compared to animal metabolism. Although the glyoxylate cycle provides evolutionary adaptations, it determines a smaller amount of energy produced per carbon atom when compared to animal catabolism of fatty acids.
Highlights
The glyoxylate cycle bypasses the decarboxylation steps of Krebs cycle and causes the assimilation of liquid carbon from acetyl-CoA
The proposed equation was validated by comparing ATP amount obtained by its application, with ATP rates obtained by the addition of ATP amount produced by oxidative phosphorylation and substrate level phosphorylation in each step of the metabolic pathways that participate in the fatty acid degradation involving the glyoxylate cycle
The energy efficiency factor in glyoxylate cycle (E%) was defined by the ratio of ATP produced in fatty acid catabolism taking into account the glyoxylate cycle and animal catabolism
Summary
The glyoxylate cycle bypasses the decarboxylation steps of Krebs cycle and causes the assimilation of liquid carbon from acetyl-CoA. Isocitrate lyase (EC 4.1.3.1) and malate synthase (EC 2.3.3.9) are the sole enzymes for this metabolic pathway. The pathway was described in 1957 during studies on microorganisms which grew on acetate and ethanol as carbon source (Kornberg & Krebs, 1957). Acetyl-CoA in the glyoxylate cycle binds with oxaloacetate, respectively producing citrate and isocitrate. The latter produces glyoxylate and succinate in the reaction catalyzed by isocitrate lyase. Glyoxylate condenses with a second acetylCoA molecule in a reaction catalyzed by malate
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