Riboflavin contains a tricyclic dimethyl-isoalloxazine ring (Flavin Nucleus) that is conjugated to a 1-Carbon ribityl, an alcohol derived from pentose sugar D-ribose, is attached at the 9 position of isoalloxazine nucleus as shown in Figure 1. The metabolically active coenzymes of riboflavin are riboflavin -5-phosphate or Flavin Mononucleotide (FMN) and flavin adenine dinucleotide (FAD) that participate in many vital oxidation reduction processes. Catalytic sites of some enzymes are covalently bound with riboflavin as prosthetic group. FAD is not strictly referred as a dinucleotide because the ribityl moiety is not attached to the isoalloxazine ring by glycosidic linkage.In FMN, the phosphoric acid is attached to ribityl alcoholic group in position 5 as
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There is a variety of amino acid residues that take part in covalent binding of flavin coenzymes to enzymes.The ribitol moiety does not take part in the redox function of flavin coenzymes. The stereochemistry and nature of the sugar alcohol, both are considered important. Some riboflavin analogs are partially active and most are inactive or having antivitamin activity, but in microbiological assays they may be active. Riboflavin is heat stable but easily degraded by light. The ribitol like moiety that is attached at position 9, can be cleaved from the vitamin, resulting in formation of lumiflavin (Figure 4) which acts as riboflavin uptake inhibitor and lumichrome (Figure 5).Both lumiflavin and lumichrome may catalyze oxidation of lipids to lipid peroxides and methionine to methional that results in the development of an unpleasant flavor known as sunlight flavor. During phototherapy for neonatal hyperbilirubinemia photolysis of riboflavin may occur. There is no evidence that normal exposure to sunlight results in significant photolysis of riboflavin, although it is possible that some of the lumichromes found in urine may arise in this
There is a variety of amino acid residues that take part in covalent binding of flavin coenzymes to enzymes.The ribitol moiety does not take part in the redox function of flavin coenzymes. The stereochemistry and nature of the sugar alcohol, both are considered important. Some riboflavin analogs are partially active and most are inactive or having antivitamin activity, but in microbiological assays they may be active. Riboflavin is heat stable but easily degraded by light. The ribitol like moiety that is attached at position 9, can be cleaved from the vitamin, resulting in formation of lumiflavin (Figure 4) which acts as riboflavin uptake inhibitor and lumichrome (Figure 5).Both lumiflavin and lumichrome may catalyze oxidation of lipids to lipid peroxides and methionine to methional that results in the development of an unpleasant flavor known as sunlight flavor. During phototherapy for neonatal hyperbilirubinemia photolysis of riboflavin may occur. There is no evidence that normal exposure to sunlight results in significant photolysis of riboflavin, although it is possible that some of the lumichromes found in urine may arise in this