Pathways

Riboflavin, also known as vitamin B2, belongs to the class of organic compounds known as flavins. These are compounds containing a flavin (7,8-dimethyl-benzo[g]pteridine-2,4-dione) moiety, with a structure characterized by an isoalloaxzine tricyclic ring. Like the other B vitamins, it supports energy production by aiding in the metabolizing of fats, carbohydrates, and proteins. Riboflavin is an important component of the cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). They act as electron carriers in a number of oxidation-reduction (redox) reactions involved in energy production and in numerous metabolic pathways including fatty acid metabolism, the citrate cycle, and the electron transport chain. Riboflavin metabolism in Arabidopsis thaliana takes place in the chloroplast and it includes two subpathways: purine metabolism and the pentose phosphate pathway. From purine metabolism, GTP is produced which is then catalyzed by GTP cyclohydrolase II to produce 2,5-diamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one which undergoes deamination to produce 5-amino-6-(5'-phosphoribosylamino)uracil and ammonia. 5-Amino-6-(5'-phosphoribosylamino)uracil gets reduced to 5-amino-6-(5-phospho-D-ribitylamino)uracil by a reductase, then 5-amino-6-(5-phospho-D-ribitylamino)uracil phosphatase removes the phosphate group from 5-amino-6-(5-phospho-D-ribitylamino)uracil to produce 5-amino-6-(1-D-ribitylamino)uracil. 5-Amino-6-(1-D-ribitylamino)uracil with L-3,4-dihydroxybutan-2-one-4-phosphate synthase then act as substrate in the reaction catalyzed by 5-amino-6-(D-ribitylamino)uracil butanedionetransferase to produce 6,7-dimethyl-8-(D-ribityl)lumazine, this which is synthesized to riboflavin and 5-amino-6-(1-D-ribitylamino)uracil. Riboflavin is then catalyzed by a riboflavin kinase to produce FMN. FMN can also get dephosphorylated back to riboflavin. In A. thaliana, FMN could also be produced by FAD nucleotidohydrolase.

Riboflavin metabolism can happen in two different sets of reactions a) Guanosine triphosphate reacts with water through a GTP cyclohydrolase resulting in the release of formic acid, pyrophosphate and 2,5-Diamino-6-(1-D-ribosylamino)pyrimidin-4(3H)-one 5'-phosphate. The latter compound then reacts with a NADH dependent 2,5-diamino-6-(ribosylamino)-4(3H)-pyrimidinone 5'-phosphate reductase resulting in the release of NAD and 2,5-Diamino-6-(1-D-ribitylamino)pyrimidin-4(3H)-one 5'-phosphate. The latter compound reacts through a tRNA pseudouridine synthase 8 / 2,5-diamino-6-(5-phospho-D-ribitylamino)-pyrimidin-4(3H)-one deaminase resulting in the release of 5-Amino-2,6-dioxy-4-(5'-phospho-D-ribitylamino)pyrimidine. b)Ribulose 5-phosphate reacts with 3,4-dihydroxy 2-butanone 4-phosphate synthase resulting in the release of formic acid and 1-Deoxy-L-glycero-tetrulose 4-phosphate. The latter compound reacts with a 5-Amino-6-ribitylamino uracil through a 6,7-dimethyl-8-ribityllumazine synthase resulting the release of 6,7-dimethyl-8-(D-ribityl)lumazine. The latter compound reacts with a riboflavin synthase resulting in the release of 5-Amino-6-ribitylamino uracil and Riboflavin. The Riboflavin reacts with an ATP driven riboflavin synthase resulting in the release of ADP and Flavin mononucleotide. The latter compound reacts with an ATP driven FAD synthetase resulting in the release of pyrophosphate and FAD.

Riboflavin (vitamin B2) is an important part of the enzyme cofactors FAD (flavin-adenine dinucleotide) and FMN (flavin mononucleotide). The name "riboflavin" actually comes from "ribose" and "flavin". Like the other B vitamins, riboflavin is needed for the breaking down and processing of ketone bodies, lipids, carbohydrates, and proteins. Riboflavin is found in many different foods, such as meats and vegetables.As the digestion process occurs, many different flavoproteins that come from food are broken down and riboflavin is reabsorbed. The reverse reaction is mediated by acid phosphatase 6. FMN can be turned into to FAD via FAD synthetase, while the reverse reaction is mediated by nucleotide pyrophosphatase. FAD and FMN are essential hydrogen carriers and are involved in over 100 redox reactions that take part in energy metabolism.

Riboflavin (vitamin B2) is an important part of the enzyme cofactors FAD (flavin-adenine dinucleotide) and FMN (flavin mononucleotide). The name "riboflavin" actually comes from "ribose" and "flavin". Like the other B vitamins, riboflavin is needed for the breaking down and processing of ketone bodies, lipids, carbohydrates, and proteins. Riboflavin is found in many different foods, such as meats and vegetables.As the digestion process occurs, many different flavoproteins that come from food are broken down and riboflavin is reabsorbed. The reverse reaction is mediated by acid phosphatase 6. FMN can be turned into to FAD via FAD synthetase, while the reverse reaction is mediated by nucleotide pyrophosphatase. FAD and FMN are essential hydrogen carriers and are involved in over 100 redox reactions that take part in energy metabolism.

The riboneogenesis pathway is in charge of converting 3 carbon units into ribose. This pathway involves the conversion of fructose 6 phosphate which can be derived from the gluconeogenesis pathway. Fructose 6 phosphate reacts with a glyceraldehyde 3 phosphate through a transketolase resulting in the release of erythrose 4 phosphate and xylulose 5 phosphate. Erythrose 4 phosphate reacts with a dihydroxyacetone phosphate resulting in a release of sedoheptulose 1,7-biphosphate. Sedoheptulose 1,7-biphosphate is transformed by SHB17 resulting in the release of sedoheptulose 7 phosphate and a phosphate. Sedoheptulose 7 phosphate reacts with a glyceraldehyde 3 phosphate through a transketolase resulting in the release of xylulose 5 phosphate and ribose 5 phosphate. Ribose 5 phosphate can react with reversibly through a ribose 5 phosphate ketol-isomerase resulting in the release of ribulose 5 phosphate. Xylulose 5 phosphate can react reversibly through a ribulose 5 phosphate 3-epimerase resulting in the release of ribulose 5 phosphate.

Escherichia coli can utilize the monosaccharide D-ribose as the sole source of carbon and energy for the cell. A high-affinity ABC transport system transports D-ribose into the cell as unphosphorylated beta-D-ribopyranose. Ribose pyranase converts between the furanose and pyranose forms of beta-D-ribose. D-ribofuranose converts between the alpha and beta anomers quickly and spontaneously. Ribokinase converts D-ribose to the pentose phosphate pathway intermediate, D-ribose 5-phosphate, which can enter the central metabolism pathways to meet the cells needs.

Escherichia coli can utilize the monosaccharide D-ribose as the sole source of carbon and energy for the cell. A high-affinity ABC transport system transports D-ribose into the cell as unphosphorylated beta-D-ribopyranose. Ribose pyranase converts between the furanose and pyranose forms of beta-D-ribose. D-ribofuranose converts between the alpha and beta anomers quickly and spontaneously. Ribokinase converts D-ribose to the pentose phosphate pathway intermediate, D-ribose 5-phosphate, which can enter the central metabolism pathways to meet the cells needs.

Escherichia coli can utilize the monosaccharide D-ribose as the sole source of carbon and energy for the cell. A high-affinity ABC transport system transports D-ribose into the cell as unphosphorylated beta-D-ribopyranose. Ribose pyranase converts between the furanose and pyranose forms of beta-D-ribose. D-ribofuranose converts between the alpha and beta anomers quickly and spontaneously. Ribokinase converts D-ribose to the pentose phosphate pathway intermediate, D-ribose 5-phosphate, which can enter the central metabolism pathways to meet the cells needs.

Escherichia coli can utilize the monosaccharide D-ribose as the sole source of carbon and energy for the cell. A high-affinity ABC transport system transports D-ribose into the cell as unphosphorylated beta-D-ribopyranose. Ribose pyranase converts between the furanose and pyranose forms of beta-D-ribose. D-ribofuranose converts between the alpha and beta anomers quickly and spontaneously. Ribokinase converts D-ribose to the pentose phosphate pathway intermediate, D-ribose 5-phosphate, which can enter the central metabolism pathways to meet the cells needs.