*B2

*'ribo' = a ribose like chain

*'flavus' = yellow

Riboflavin Structure

*Wide-variety 

*Milk/dairy

*Legumes

*Green veg (spinach)

*Grains (whole and fortified)- as FMN or FAD

*Heat-stable

*Light-sensitive

Flavocoenzyme FMN

Flavocoenzyme FAD

*Riboflavin that's attached non-covalently to proteins is digested by HCl, gastric and intestinal enzymes

*FAD and FMN = digested in intestinal lumen

*~7% of FAD in food is covalently bound either to His or Cys residues --> excreted in urine

*Animal sources > plant sources

*Metals (such as Cu2+, Zn2+, Fe2+, Mn2+) can bind to riboflavin and FMN = decrease riboflavin absorption

*Alcohol ingestion = decrease riboflavin digestion and absorption  

*Na⁺- dep transport

*Simple diffusion at high doses

*Inside intestinal cell, riboflavin is phosphorylated to FMN

*Only free riboflavin can cross most cell membranes by carrier-mediated process via RBP (Riboflavin binding protein)

*Inside cells, phosphorylated to FMN and FAD

-Hormones increase flavokinase activity, accelerate FMN/FAD synthesis

-Cellular content of FMN and FAD tightly regulated product feedback

*Flavoproteins: FMN and FAD become bound to enzymes

*Little storage

*Excretion reflects intake

*Primarily in urine as riboflavin

*Non-protein bound riboflavin in plasma- filtered by kidney and excreted

*Excretion is increased with diabetes, trauma, stress

*Energy production

*Enzyme operations

*Nerve function

*Liver metabolism

*Coenzymes that function in redox rxns involved in catabolism of glucose, FAs, ketone bodies, and AAs

*FAD and FMN are coupled to e-/oxygen transfer systems

-Oxidizing and Reducing agents (FAD/FADH₂)

*Either FADH₂ or NADH are initial H⁺ acceptors for ETC

*The e^- and H⁺s are enzymatically transferred through the ETC components and eventually to O^-, which is reduced to H₂O

Decarboxylation of pyruvate (PDH) 

FADH₂ and Succinate in TCA

Fatty acyl CoA dehydrogenase requires FAD in FA oxidation

*RDA Men = 1.3mg/d

*RDA Women = 1.1mg/d

-Riboflavin is important in energy metabolism, recommended intake varies according to energy intake

*Measure erythrocyte glutathione reductase activity

*Usually with other deficiencies

*Cheilosis: lesions on lips

*Angular stomatitis: lesions on corners of mouth

*Stomatitis: inflammation of mucosal lining in oral cavity

*Glossitis: inflammation of tongue

*Hyperemia and Edema of oral cavity: increased blood and swelling

*Severe deficiency can impair synthesis of B₆ and niacin

*Protein and DNA damage, arresting cell cycle

*Susceptible populations to deficiency:

-Ppl w/congenital heart disease, some cancers, alcoholics

-Women on oral contraceptives

-People who have a base pair mutation in methylene tetrahydrofolate reductase

*Low risk of toxicity

*No cases reported ever

UL not determined