Guanosine monophosphate (GMP)

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.^[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 catalyzesThe phosphate inventory is conserved: $3+1=2+2$. In an idealized closed mixture initially containing $2\mu \mathrm{mol}$ of ATP and $1\mu \mathrm{mol}$ of GMP, at most $1\mu \mathrm{mol}$ can proceed through the forward reaction before GMP is exhausted, absent other reactions. This is a stoichiometric upper bound rather than an equilibrium prediction.^[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.^[ref]