Riboflavin Flashcards
What are the properties of riboflavin? what is its function? what is it also known as?
water-soluble vitamin critical for energy metabolism, redox reactions, and enzyme function.
-Riboflavin is also known as Vitamin B2.
How is riboflavin affected by light and heat?
Heat stable but unstable in UV light and alkaline solutions.
This instability is why milk, a major source of riboflavin, is stored in opaque containers.
What are the active coenzyme forms of riboflavin?
- FMN (Flavin Mononucleotide)
- FAD (Flavin Adenine Dinucleotide)
FMN is converted to riboflavin-5-phosphate, and FAD to riboflavin-5-adenosyl-diphosphate.
What role does thyroid hormone play in riboflavin metabolism?
It increases flavokinase activity, regulating the conversion of riboflavin into FMN and FAD.
what is the structural distinction between Riboflavin, FAD and FMN?
riboflavin is a structural unit contained within both FMN/FAD
-FAD is FMN with an AMP group attached
What role does riboflavin play in energy metabolism?
-TCA cycle, ETC, β-oxidation
-Detoxification
-Regulation of redox status
-Conversion of B6/folate into coenzyme
-synthesis of niacin from Trp
Examples include pyruvate dehydrogenase complex and succinate dehydrogenase.
What is the function of riboflavin in redox reactions?
FMN and FAD act as electron carriers, accepting and donating hydrogen atoms, regulating cellular redox status.
what is the role of riboflavin in beta oxidation?
FAD used as a prostethic group to generate FADH2
Which vitamins require riboflavin for activation?
- Vitamin B6 (Pyridoxine)
- Folate (B9)
- Niacin (B3)
FAD is necessary for the conversion of tryptophan into niacin.
explain how riboflavin is absorbed in the body. what transporters are involved?
1) FMN/FAD attached to proteins is broken down by proteases to release free FAD/FMN
2) phosphatase removes a phosphate to convert it to riboflavin-allowing it to be absorbed into cells through RFT1/2 transporters
3) riboflavin phosphorylated and stored as FMN/FAD
4) converted back to riboflavin for portal ciurculation
low intake: carrier mediated transport
high intake: diffusion across membrane
How is riboflavin transported in the plasma?
As free riboflavin and some FMN, mostly bound to plasma proteins like albumin.
What is the storage capacity for riboflavin in the body?
Limited storage capacity; highest concentrations are in the liver, kidneys, and heart.
What happens to excess riboflavin in the body?
Excess riboflavin is excreted in urine, leading to bright yellow urine with high-dose supplements
-limited storage -> excretion reflects intake
What are food sources of riboflavin? what form is it mainly found in?
- Dairy products (milk, cheese, yogurt, eggs)
- Meat (liver, kidney, lean meats, fish)
- Green leafy vegetables (spinach, kale)
- Enriched grains & breakfast cereals
-mainly found as FAD
Gut bacteria in the large intestine can synthesize riboflavin, but absorption is unclear.
What factors affect the bioavailability of riboflavin?
Related to digestibility of food
-dairy & meat sources have higher bioavailability than plant sources
-alcohol reduces absorption.
What are the signs and symptoms of riboflavin deficiency? what is this called?
- Growth retardation
- Fatigue
- Cheilosis
- Glossitis
- Angular stomatitis
- Dermatitis
- Corneal vascularization
- Neurological symptoms
-Ariboflavinosis
similar symptoms to B6 deficiency
How is riboflavin status tested? what values indicate deficiency?
By measuring glutathione reductase acitivity (EGRAC coefficient)
-similar to TPP; increased acitivity with addition of FAD this indicates low saturation of FAD in blood
->40^% indicates deficient
Normal: <20% increase; Marginal: 20-40% increase; Deficient: >40% increase.
Who are the populations at risk for riboflavin deficiency?
- Elderly
- Pregnant & lactating women
- People with thyroid disease
- Diabetes patients
- Hyperbilirubinemia (jaundice) patients
- Vegetarians & vegans
These groups may have increased needs or reduced intake.
What is the RDA for riboflavin? What is the upper limit (UL)?
RDA depends on energy intake (atleast 1mg neede)
-No UL set because toxicity is rare; excess is rapidly excreted.
What other nutrient deficiencies are associated with riboflavin deficiency? how is riboflavin involved?
Iron: flavins needed to reduce Fe3+ to Fe2+
Vit B6 (pyridoxine): FMN required to convert to active form
Folate: flavin needed to oxize folate
