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Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a "keto group" (a lactam) and an amino group on positions 4 and 2 respectively. It is structurally related to the parent bicyclic heterocycle called pteridine. Pterins, as a group, are compounds related to pterin with additional substituents. Pterin itself is of no biological significance.
Pterins were first discovered in the pigments of butterfly wings (hence the origin of their name, from the Greek pteron (πτερόν), wing) and perform many roles in coloration in the biological world.
Pterins exhibit a wide range of tautomerism in water, beyond what is assumed by just keto-enol tautomerism. For the unsubstituted pterin, at least five tautomers are commonly cited. For 6-methylpterin, seven tautomers are theoretically predicted to be important in solution.
The pteridine ring system contains four nitrogen atoms, reducing its aromaticity to the point that it can be attacked by nucleophile. Pterins can take three oxidation states on the ring system: the unprefixed oxidized form, the 7,8-dihydro semi-reduced form (among other, less stable tautomers), and finally the 5,6,7,8-tetrahydro fully-reduced form. The latter two are more common in biological systems.
The above series of structures shows 5 of the possible tautomers of pterin. They only differ in the position of hydrogen atoms on oxygen or nitrogen. In water, and thus biological systems, this structures are in a fast equilibrium, meaning each of the structures might be present to perform a reaction. Although the pattern of single and double bonds in the ring system changes with the position of the hydrogen atoms, the overall π-system does not change. What does change is the charge distribution and hence the possible reactions of the species. With respect to reaction speed, if a single tautomer is required, each molecule spends part of its time as one of the tautomers. This might reduce the speed of reaction, leaving a very fast (enzymatic!) reaction just to be fast.
Pterin rings are either salvaged from existing ones or produced de novo in living organisms. The ring comes from rearrangement of guanosine in bacteria and humans.
Pterin derivatives are common cofactors in all domains of life.
One important family of pterin derivatives are folates. Folates are pterins that contain p-aminobenzoic acid connected to the methyl group at position 6 of the pteridine ring system (known as pteroic acid) conjugated with one or more L-glutamates. They participate in numerous biological group transfer reactions. Folate-dependent biosynthetic reactions include the transfer of methyl groups from 5-methyltetrahydrofolate to homocysteine to form L-methionine, and the transfer of formyl groups from 10-formyltetrahydrofolate to L-methionine to form N-formylmethionine in initiator tRNAs. Folates are also essential for the biosynthesis of purines and one pyrimidine.
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Pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a "keto group" (a lactam) and an amino group on positions 4 and 2 respectively. It is structurally related to the parent bicyclic heterocycle called pteridine. Pterins, as a group, are compounds related to pterin with additional substituents. Pterin itself is of no biological significance.
Pterins were first discovered in the pigments of butterfly wings (hence the origin of their name, from the Greek pteron (πτερόν), wing) and perform many roles in coloration in the biological world.
Pterins exhibit a wide range of tautomerism in water, beyond what is assumed by just keto-enol tautomerism. For the unsubstituted pterin, at least five tautomers are commonly cited. For 6-methylpterin, seven tautomers are theoretically predicted to be important in solution.
The pteridine ring system contains four nitrogen atoms, reducing its aromaticity to the point that it can be attacked by nucleophile. Pterins can take three oxidation states on the ring system: the unprefixed oxidized form, the 7,8-dihydro semi-reduced form (among other, less stable tautomers), and finally the 5,6,7,8-tetrahydro fully-reduced form. The latter two are more common in biological systems.
The above series of structures shows 5 of the possible tautomers of pterin. They only differ in the position of hydrogen atoms on oxygen or nitrogen. In water, and thus biological systems, this structures are in a fast equilibrium, meaning each of the structures might be present to perform a reaction. Although the pattern of single and double bonds in the ring system changes with the position of the hydrogen atoms, the overall π-system does not change. What does change is the charge distribution and hence the possible reactions of the species. With respect to reaction speed, if a single tautomer is required, each molecule spends part of its time as one of the tautomers. This might reduce the speed of reaction, leaving a very fast (enzymatic!) reaction just to be fast.
Pterin rings are either salvaged from existing ones or produced de novo in living organisms. The ring comes from rearrangement of guanosine in bacteria and humans.
Pterin derivatives are common cofactors in all domains of life.
One important family of pterin derivatives are folates. Folates are pterins that contain p-aminobenzoic acid connected to the methyl group at position 6 of the pteridine ring system (known as pteroic acid) conjugated with one or more L-glutamates. They participate in numerous biological group transfer reactions. Folate-dependent biosynthetic reactions include the transfer of methyl groups from 5-methyltetrahydrofolate to homocysteine to form L-methionine, and the transfer of formyl groups from 10-formyltetrahydrofolate to L-methionine to form N-formylmethionine in initiator tRNAs. Folates are also essential for the biosynthesis of purines and one pyrimidine.