Anaplerotic reactions

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Anaplerotic reactions are those that form intermediates of the TCA or citric acid cycle. As this is a cycle, formation of any of the intermediates can be used to 'top up' the whole cycle. Anaplerotic is of Greek origin, meaning "to fill up".

There are 4 reactions classed as anaplerotic, although the production of oxaloacetate from pyruvate is probably the most important physiologically.

From	To	Reaction	Notes
Pyruvate	oxaloacetate	pyruvate + CO2 + H2O + ATP $\longrightarrow$ oxaloacetate + ADP + Pi + 2H+	This reaction is catalysed by pyruvate carboxylase, an enzyme activated by Acetyl-CoA, indicating a lack of oxaloacetate. Pyruvate can also be converted to L-malate, another intermediate, in a similar way.
Aspartate	oxaloacetate	-	This is a reversible reaction forming oxaloacetate from aspartate in a transamination reaction, via aspartate transaminase.
Glutamate	α-ketoglutarate	glutamate + NAD+ + H2O $\longrightarrow$ NH4+ + α-ketoglutarate + NADH + H+.	This reaction is catalysed by glutamate-dehydrogenase.
β-oxidation of fatty acids	succinyl-CoA	-	When odd-chain fatty acids are oxidized, one molecule of succinyl-CoA is formed per fatty acid. The final enzyme is methylmalonyl-CoA mutase.

External links

• Owen O, Kalhan S, Hanson R (2002). The key role of anaplerosis and cataplerosis for citric acid cycle function. J. Biol. Chem. 277 (34): 30409-12.

de:Anaplerotische Reaktionen