The cycle comprises three enzyme-catalysed reactions. The first stage is the deamination of the purine nucleotide adenosine monophosphate (AMP) to form inosine monophosphate (IMP), catalysed by the enzyme AMP deaminase:
:AMP + HO + H → IMP + NH
The second stage is the formation of adenylosuccinate from IMP and the amino acid aspartate, which is coupled to the energetically favourable hydrolysis of GTP, and catalysed by the enzyme adenylosuccinate synthetase:
:Aspartate + IMP + GTP → Adenylosuccinate + GDP + P
Finally, adenylosuccinate is cleaved by the enzyme adenylosuccinate lyase to release fumarate and regenerate the starting material of AMP:
:Adenylosuccinate → AMP + Fumarate
A recent study showed that activation of HIF-1α allows cardiomyocytes to sustain mitochondrial membrane potential during anoxic stress by utilizing fumarate produced by adenylosuccinate lyase as an alternate terminal electron acceptor in place of oxygen. This mechanism should help provide protection in the ischemic heart.