Riboflavin B2 Ribo stands for the ribose like structure and flavus stands for yellow in Latin Riboflavin is what causes the bright yellow color to urine There was a picture on this about Ariboflavinosis with scaly sores around the tongue and mouth Our food sources are dietary products meat eggs legumes beans green vegetables and Riboflavin has Ribitol side chain and Flavin isoalloxazine ring We can use two forms FMN enriched cereals and bread The higher quantity sources are named first Flavin mononucleotide and FAD Flavin adenine dinucleotide Riboflavin FMN FAD reversible two step reaction Riboflavin is one of the easiest destroyed B vitamins by light That is why milk is in an opaque and not a clear container When you have neonatal infants with too much Bilirubin or Jaundice they are given a riboflavin supplement this is usually called phosphorylated form This is Riboflavin in the vitamin form FMN is gotten from the addition of a phosphate to Riboflavin So the Coenzyme form such as FAD is gotten from the addition of a phosphate and adenine of FMN This is Co enzyme form Digestion and absorption It is eaten in all forms including Riboflavin FAD FMN and riboflavin Intestine Digestion involves continuation of freeing riboflavin from proteins by intestinal phosphate In the stomach riboflavin is freed from proteins by HCl and gastric enzymes enzymes We also see FA and FMN being converted to Riboflavin FAD FMN riboflavin The first enzyme associated with the two step reaction is FAD pyro phosphatase and then FMN phosphatase Riboflavin phosphate is hydrolyzed by phosphatases to riboflavin So no matter which form is used you can get it down to free riboflavin for transport into the enterocyte Absorption of riboflavin in intestine is at proximal duodenum or jejunum Rate proportionate to dose large amounts diffusion small amounts carrier system Riboflavin then enters portal system In the bloodstream you have riboflavin FAD and FMN bound to Albumin not free Co enzyme transportation with the Albumin but must still be converted into vitamin to get into the cell In the tissues free riboflavin is absorbed at most cell membranes and then once inside cell converted to Co enzyme forms ATP ADP ATP ADP Riboflavin FMN FAD FAD is a Co enzyme FAD turns to FADH and then enters ETC FAHD2 is the same thing This class We see FAD FADH in Krebs s cycle with Succinate Dehydrogenase Flavokinase FAD synthase says it forms 2 ATP Another reaction involving FAD is Pyruvate Acetyl CoA The reaction involves TPP thiamin FAD riboflavin and NAD niacin ketoglutarate Succinyl CoA has a very similar pathway This cycle is considered a hidden reaction http www coenzyme a com tca html In the mitochondria oxidation also uses FAD when we go from a fatty acyl CoA to Enoyl CoA with fatty acyl CoA dehydrogenase oxidation itself produces 1 NADH and 1 FADH which is 5 ATP What else is riboflavin involved in Neurotransmitters deamination of NT uses enzyme monoamine oxidase which requires FAD MAOI s are medication to help with depression and anxiety This allows NT to stay active and help by blocking the enzyme stated above Vitamin B6 metabolism pyridoxial 4 pyridoxic acid and or 2 Co enzymes PLP requires FAD and FMN Folate metabolism requires FADH2 Synthesis of Niacin from Tryptophan requires FAD so being deficient in riboflavin can cause a problem with Niacin Lastly Glutathione GSSG acts like antioxidant to GSH using Glutathione Reductase requires FAD We know that Riboflavin FAD using ETC produces 2 ATP Remember that 2 is not a proton pump but just attached to Ubiquinone for transferring of electrons FMN is actually within complex I It won t shuttle between metabolic systems or ETC Inside the complex is Niacin drops off proton to FMN which then passes them to Fe Electrons are dissociated and are then picked up by Ubiquinone So riboflavin in ETC is functioning in two different places and in two different forms Assessment of status How would we know if we have enough Riboflavin Erythrocyte glutathione Reductase ERG and by urinary riboflavin excretion If we have the ERG enzyme then we have plenty of it indirectly In the urine it is excreted primarily as free Riboflavin The difficulty here of the two tests is Absorbed Utilized Cons Blood YES YES Indirect measure Urine YES We can t tell Can t tell if it was utilized through the urine Deficiency is Ariboflavinosis It usually occurs with other deficiencies because of the variety of food sources Symptoms include Cheilosis cracking around mouth angular stomatitis and glossitis inflammation of tongue Other symptoms include Seborrheic dermatitis Anemia and peripheral nerve dysfunction This deficiency can inhibit synthesis of niacin from tryptophan and B6 metabolism These are MULTITEP problems not direct links Those at risk Congenital heart disease some cancers excess alcohol intake due to poor dietary intake those in developing countries where grains are not fortified Thyroid disease and Diabetes Toxicity has no UL
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