Riboflavin (B2) Flashcards
what are the coenzyme forms of riboflavin (B2)?
- flavin adenine dinucleotide (FAD)
- flavin mononucleotide (FMN)
what are the functions of riboflavin coenzyme form?
- function as electron transfer reaction (2-step single-electron reactions)
- energy production in the TCA cycle, electron transport chain and fatty acid oxidation
what is the role of free Riboflavin (B2)?
acts as a non-coenzyme form that is absorbed and transported throughout the body
DNA synthesis, antioxidant function (glutathione reductase)
how is riboflavin transported in the tissue cells?
transported in its “free form” and converted to FAD/FMN in tissue cells via ATP-dependent reactions. The FAD form becomes free riboflavin in the lumen.
what are the two enzymes that make up riboflavin (free form)?
flavin and ribitol
what does FMN stand for?
flavin mononucleotide
what does FAD stand for?
flavin adenine dinucleotide
what are the sources of riboflavin?
milk/dairy, eggs, meats, spinach, legumes, mushrooms, and enriched cereals/breads
what are the functions of riboflavin?
- coenzyme in flavoproteins
- energy transformation (ETC, oxidative decarboxylation of pyruvate and a-ketoglutarate, TCA cycle, and fatty acid oxidation)
- reducing enzymes (NADPH, FAD-dependent reductase)
______ is the coenzyme used to combine with oxidized ________ into reduced glutathione (NADP+) + 2 GSH
FAD; glutathione
what are the electron donors in glutathione reductase?
NADPH
why is glutathione reductase essential?
maintains glutathione in reduced state (GSH)
GSH is a key endogenous antioxidant for what (3) things?
- maintaining SH group in proteins
- maintaining heme in Fe2+ state
- removal of toxic peroxides
what is thioredoxin reductase (TrxR)?
flavoenzyme that reduces thioredoxin
what is thioredoxin (Trx)?
proteins acting as antioxidants by facilitating the reduction of other proteins by cysteine thiol-disulfide exchange
what are the purposes of thioredoxins?
- helps ribonucleotide reductase to make DNA
- electron donor (SH) to ribonucleotide
- used to regenerate S to SH
how is riboflavin digested, absorbed and transported through the body?
- FAD/FMN (coenzyme) in foods are hydrolyzed by phosphatases within the intestinal lumen (converts to free form)
- carrier-mediated and energy-depended processes absorb the free-form
- after absorption, free riboflavin is transported in the blood and converted back to the coenzyme form (FAD/FMN) and congregates in the liver, kidney, and heart
- coenzyme form are bound to apoenzyme and function as prosthetic groups for oxidation-reduction reactions
how is the free form of riboflavin converted back to its coenzyme form after absorption?
ATP-dependent reactions (in tissue cells)
how is riboflavin excreted out the body?
primarily in urine with small amount in feces
what is the deficiency of riboflavin and what individuals have higher risk?
- ariboflavinosis (acute)
- individuals with homozygous mutation MTHFR, 677TT
large doses of riboflavin are known to treat what?
migraine headaches
how do we assess nutritional status of B2?
- by measuring the activity of erythrocyte glutathione reductase (if limited activity, an individual has a deficiency)
- AC 1.1.2 = normal
- AC >1.4 = deficiency
what are the key enzymes riboflavin is involved in?
- succinate dehydrogenase
- glutathione reductase
- thioredoxin reductase
what are the physiological processes riboflavin is involved in?
- electron transport chain
- fatty acid oxidation
- redox reactions
