Anabolism of Inosine Monophosphate

AMP synthesis (The two reactions of AMP synthesis minic steps in the purine pathway leading to IMP.) In Step 1, the 6-0 of inosine is displaced by aspartate to yield adenylosuccinate. The energy required to drive this reaction is derived from GTP hydrolysis. The enzyme is adenylosuccinate synthetase. 

AMP is a competitive inhibitor (with respect to the substrate IMP) of adenylosuccinate synthetase. 

In Step 2, adenylosuccinase (also known as adenylosuccinate lyase, the same enzyme that catalyzes one of the steps in the purine pathway) carries out the nonhydrolytic removal of fumarate from adenylosuccinate, leaving AMP. 

GMP synthesis The two reactions of GMP synthesis are an NAD -dependent oxidation followed by an amidotransferase reaction. In Step 1, IMP dehydrogenase employs the substrates NAD and H2O in catalyzing oxidation of IMP at C-2. The products are xanthylic acid (XMP or xanthosine monophosphate), NADH, and H. GMP is a competitive inhibitor (with respect to IMP) of IMP dehydrogenase. In Step 2, transfer of the amido-N of glutamine to the C-2 position of XMP yields GMP. This ATP-dependent reaction is catalyzed by GMP synthetase. 

and PP . Hydrolysis of PPj to 2 Pj by pyrophosphatases drives this reaction to completion. 

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