Guanosine monophosphate

GMP synthesis starts with D-ribose 5′-phosphate, a product of the pentose phosphate pathway. The synthesis proceeds by the gradual formation of the purine ring on carbon-1 of ribose, with CO₂, glutamine, glycine, aspartate and one-carbon derivatives of tetrahydrofolate donating various elements towards the building of the ring.^[2]

 

As inhibitor of guanosine monophosphate synthesis in experimental models, the glutamine analogue DON can be used.^[3]

GMP can also exist as a cyclic structure known as cyclic GMP. Within certain cells the enzyme guanylyl cyclase makes cGMP from GTP.

cGMP plays an important role in mediating hormonal signaling.^[2]

GMP was originally identified as the umami substance in dried shiitake mushroom. The drying process significantly increases GMP content with the breakdown of RNA. It can be found in a number of other mushrooms.^[4]

Industrial production is based on fermentation: a bacterium converts sugars into AICA ribonucleotide, which is then converted chemically to GMP.^[5] Tapioca starch is a possible sugar source.^[6]

Guanosine monophosphate is known as E number reference E626.^[7] In the form of its salts, such as disodium guanylate (E627), dipotassium guanylate (E628) and calcium guanylate (E629), are food additives used as flavor enhancers to provide the umami taste.^[7] It is often used in synergy with disodium inosinate; the combination is known as disodium 5′-ribonucleotides. Disodium guanylate is often found in instant noodles, potato chips and snacks, savoury rice, tinned vegetables, cured meats, and packet soup.

As it is a fairly expensive additive, it is usually not used independently of glutamic acid or monosodium glutamate (MSG), which also contribute umami. If inosinate and guanylate salts are present in a list of ingredients but MSG does not appear to be, the glutamic acid is likely provided as part of another ingredient, such as a processed soy protein complex (hydrolyzed soy protein), autolyzed yeast, or soy sauce.