= Guanosine monophosphate
{title2=GMP}
\b[Guanosine monophosphate], conventionally GMP in biochemical contexts, is the 5′-monophosphate of <guanosine>. It combines the <nucleobase> <guanine>, the <sugar> <ribose> and one phosphate group, making it a purine <ribonucleotide>. The named position matters: it specifies where the phosphate is attached.<Guanosine Monophosphate in PubChem>[Single-compound CID 135398631: guanosine 5′-phosphate and purine ribonucleoside monophosphate.]{ref}
The related names encode different chemical distinctions. <Guanine> is the base; <guanosine> adds the ribose; <guanosine monophosphate> adds phosphate. <Cyclic guanosine monophosphate> instead has a cyclic phosphate linkage, while <guanosine diphosphate> and <guanosine triphosphate> contain two and three phosphate groups. Similar abbreviations do not make them interchangeable molecular signals.
GMP is a substrate in nucleotide metabolism. <Guanylate kinase> catalyzes
$$
\mathrm{ATP+GMP\rightleftharpoons ADP+GDP}.
$$
The phosphate inventory is conserved: $3+1=2+2$. In an idealized closed mixture initially containing $2\,\mathrm{\mu mol}$ of ATP and $1\,\mathrm{\mu mol}$ of GMP, at most $1\,\mathrm{\mu mol}$ can proceed through the forward reaction before GMP is exhausted, absent other reactions. This is a stoichiometric upper bound rather than an equilibrium prediction.<Cloning and expression of the essential gene for guanylate kinase from yeast by M. Konrad>[Abstract: reversible transfer of ATP's terminal phosphoryl group to GMP.]{ref}
The yeast study isolated and characterized the <guanylate kinase> gene using sequence information from the enzyme. It connects a chemically defined substrate to an experimentally identifiable molecular catalyst; it does not mean that a gene sequence alone measures the amount of GMP present in a cell.<Cloning and expression of the essential gene for guanylate kinase from yeast by M. Konrad>[Isolation and characterization of Saccharomyces cerevisiae GUK1.]{ref}
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