Guanosine is a purine nucleoside made up of a guanine moiety attached to a ribose ring through a β-N9-glycosidic bond. Guanosine can be converted to guanosine monophosphate (GMP), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP), and guanosine triphosphate (GTP) by the process of phosphoryation. These phosphorylated forms of guanosine play key roles in the processes of nucleic acid and protein synthesis, photosynthesis, muscle contraction, and intracellular signal transduction (specifically with cGMP).
Guanosine is required in mRNA for an RNA splicing reaction. When a "self-splicing" intron excises itself from the mRNA message (requiring a 5’ guanosine) cutting at both ends, re-ligating, and leaving just the exons on either side to be translated into a functional protein. The antiviral drug acyclovir, which is used in the treatment of herpes, and the anti-HIV drug abacavir are both structurally similar to guanosine. Guanosine was also used to make regadenoson, an A2A adenosine receptor agonist that is a coronary vasodilator and is often used in pharmacologic stress testing. Guanosine prevents Quinolinic Acid (QA) induced seizures about as well as the NMDA receptor antagonist, MK-801. Besides acting as an NMDA receptor agonist, QA decreases glutamate transport/uptake. It has been shown that Guanosine counteracts the QA-induced decrease in glutamate uptake as well as increases in glutamate release from the synapse.