Riboflavin B2 Review

RIBOFLAVIN (B2)

Structure:

• Flavin - yellow colored, seen in urine
• Ribitol

Coenzymes:

• FMN
• FAD

SOURCES

DIGESTION, ABSORPTION, METABOLISM, and EXCRETION

FUNCTION/MOA

2 coenzyme forms of Riboflavin - FAD FMN

• Flavoproteins exhibit a wide range of redox potentials so can play a variety of roles in intermediary metabolism
• FAD and FMN have ability to accept a pair of hydrogen atoms
• Reduction of FAD and FMN results in FADH2 and FMNH2

Role in Nutrition and Energy Production

• Electron transport chain
• B6 metabolism
• Pyridoxine phosphate oxidase (converts PMP and PNP to PLP, dependant on FMN)
• L-amino oxidase uses FMN in the dehydrogenase of L-amino acids to imino acids
• Oxidative decarboxylation of pyruvate and a-ketoglutarate
• Succinate dehydrogenase removes electrons from succinic acid to form fumarate
• Fatty acid beta-oxidation, acyl-coA dehydrogenase requires FAD
• Sphingonine oxidase, requires FADA
• Coenzyme for an oxidase such as Xanthine Oxidase involved in purine metabolism
• Aldehyde oxidate
• Synthesis of folate
• Synthesis of niacin from tryptophan
• Choline metabolism
• Monoamine oxidate (dopamine)
• Glutathione reductase 
• Eral and sulfhydryl oxidases, impair folding with B2 deficiency
• THioredoxin reductase
• Ribonucleotide reductase
• Hydrogen peroxide production from O2

USES

• Migraine headaches 400 mg
• Glutaric acid type 1
• Beta-oxidation of fatty acids in mitochondria

RDA

1.3 mg/d and 1.1 mg/d

Deficiency

Ariboflavinosis

• 3-4 months of inadequate intake
• cheliosis, angular stomatitis, glossitis
• skin becomes reddened scaly greasy painful
• conjuctivitis
• neuropathy
• RXb5-30mg daily

At risk: etoh, hypothyroidism, adrenal insufficiency, DM, trauma, stress, TCAs

Toxicity

no TUL

Assessment

Measurement of activity of FAD-dependent enzyme erythrocyte glutathione reductase

• Activity Coefficients
• AC 1.2 to 1.4 normal
• AC>1.4 riboflavin deficiency

FAD-dependent enzyme pyridoxamine phosphate oxidase

Urinary riboflavin excretion with <25 ug/g creatinine = deficiency