'Furthermore, it is likely that carbons 4, 3a, and 8a from the lumazine are transferred as a unit to the unknown compound since in experiments with 6.7-dimethyl-8-ribityllumazine-4,8a-C radioactivity is recovered in oxomalonic acid. It is not clear at the moment whether the separation of ribitylamine and the remainder of the heterocyclic ring derived from 6,7-dimethyl-8-ribityllumazine occurs during the enzymic conversion of the lumazine to riboflavin or whether it is due to secondary chemical decomposition occurring during the separation process.
Some evidence suggests that the latter is true and that the primary product formed during enzymic action is a very unstable compound which cleaves easily to ribityllumazine and into the remainder of the heterocyclic ring system of the lumazine....The preceding experiments have demonstrated that the chemical changes which are catalyzed by riboflavin synthetase involves the heterocyclic ring system of the lumazine....It can be seen that substitution of the ribityl group by a methyl or beta-hydroxyethyl group does not lead to the formation of an analogous flavin. Furthermore, all of the epimeric forms of the tetrahydropentylo derivatives have now been synthesized in collaboration with Dr. Winestock (except the L-ribityl compound).
These pentyl analogs as well as the corresponding glucityl, mannityl, and galactityl derivatives are not convertible to the corresponding isoalloxazine compounds. However, this does not mean that these compounds cannot react with the enzyme. Thus, as can be seen in Fig. 9, 6.7-dimethyl-8-D-xylityllumazine inhibits the conversion of 6.7-dimethyl-8-ribityllumazine to riboflavin competitively. Another potent inhibitor in this series is 6.7-dimethyl-8-D-5'-deoxyribityllumazine. However, the behavior of this compound differs from that of the D-xylityl derivative in that (a) the inhibition is not competitive with the ribityllumazine derivative and (b) it is the only substance we have found so far which is converted at a very slow rate to the corresponding isoalloxazine, namely, 5'-deoxyriboflavin.'
This 5'-deoxyriboflavin moiety is comparable to riboflavin provisioning in the Colias-Wolbachia assemblage as well as the dNTP precursor including the deoxyguanosine kinase mutation in MDS.
Some evidence suggests that the latter is true and that the primary product formed during enzymic action is a very unstable compound which cleaves easily to ribityllumazine and into the remainder of the heterocyclic ring system of the lumazine....The preceding experiments have demonstrated that the chemical changes which are catalyzed by riboflavin synthetase involves the heterocyclic ring system of the lumazine....It can be seen that substitution of the ribityl group by a methyl or beta-hydroxyethyl group does not lead to the formation of an analogous flavin. Furthermore, all of the epimeric forms of the tetrahydropentylo derivatives have now been synthesized in collaboration with Dr. Winestock (except the L-ribityl compound).
These pentyl analogs as well as the corresponding glucityl, mannityl, and galactityl derivatives are not convertible to the corresponding isoalloxazine compounds. However, this does not mean that these compounds cannot react with the enzyme. Thus, as can be seen in Fig. 9, 6.7-dimethyl-8-D-xylityllumazine inhibits the conversion of 6.7-dimethyl-8-ribityllumazine to riboflavin competitively. Another potent inhibitor in this series is 6.7-dimethyl-8-D-5'-deoxyribityllumazine. However, the behavior of this compound differs from that of the D-xylityl derivative in that (a) the inhibition is not competitive with the ribityllumazine derivative and (b) it is the only substance we have found so far which is converted at a very slow rate to the corresponding isoalloxazine, namely, 5'-deoxyriboflavin.'
This 5'-deoxyriboflavin moiety is comparable to riboflavin provisioning in the Colias-Wolbachia assemblage as well as the dNTP precursor including the deoxyguanosine kinase mutation in MDS.
