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 References