The synthesis of guanosine monophosphate (GMP) from inosine monophosphate (IMP) involves adding a ketone and then aminating it. The process occurs in two steps:

1. IMP is oxidized with NAD+ and H2O to form xanthylate:
$$ \text{IMP} + \text{H}_2\text{O} + \text{NAD}^+ \rightarrow \text{Xanthylate} + \text{NADH} + \text{H}^+ $$
2. Xanthylate reacts with ATP and ammonia (derived from the hydrolysis of glutamine) to produce guanylate (GMP) and glutamate.

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In the purine de novo synthesis pathway, inosine monophosphate (IMP, also known as inosinate) serves as a common intermediate for synthesizing adenosine monophosphate (AMP) and guanosine monophosphate (GMP). The conversion of IMP to either AMP or GMP involves aminating the molecule. To synthesize AMP, a ketone group is replaced with an amino group. To synthesize GMP, another ketone group is added and subsequently aminated.

Synthesis of AMP and GMP from Inosine Monophosphate (IMP)

The synthesis of adenosine monophosphate (AMP) from inosine monophosphate (IMP) replaces a ketone with an amino group. GTP provides the phosphoryl group, and aspartate provides the amino group. The process occurs in two steps:

1. IMP, GTP, and aspartate react to form adenylosuccinate:
$$ \text{IMP} + \text{GTP} + \text{Aspartate} \rightarrow \text{Adenylosuccinate} + \text{GDP} + \text{P}_i $$
2. Adenylosuccinate is cleaved to yield adenylate (AMP) and fumarate:
$$ \text{Adenylosuccinate} \rightarrow \text{AMP} + \text{Fumarate} $$

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