Nutrition Lecture 9: Riboflavin Flashcards
What are rich sources of riboflavin?
Main source = dairy products
Fortified sources: weet-bix, soy milk
What is the structure of riboflavin?
Ribose sugar and Flavin structure
What does riboflavin look like?
A yellow-orange crystalline solid
What is riboflavin rapidly inactivated by?
UV and visible light
What is the solubility of riboflavin?
Poor solubility in water compared to other B-vitamins
What is the bioavailability of riboflavin?
High - 95% absorbed
When does riboflavin absorption decline?
High doses > 27 mg
Where is most riboflavin absorbed?
In proximal small intestine
How is riboflavin absorbed into and out of enterocytes?
via riboflavin vitamin transporters (RFVT)
How are high doses of riboflavin absorbed?
by passive diffusion
How is riboflavin transported?
On proteins - primarily albumin
Where is riboflavin stored?
Stored in only small amounts in the liver, heart and kidney - enough for 2-6 weeks
What is the main function of riboflavin?
An integral component of flavocoenzymes
What are flavocoenzymes?
a group of enzymes that contain flavin cofactors derived from riboflavin (vitamin B2)
What are the flavocoenzymes that riboflavin are part of? (2)
FMN and FAD
What does FMN stand for?
Flavin mononucleotide
What does FAD stand for?
Flavin adenine dinucleotide
What is the more common flavocoenzyme that riboflavin is converted into?
FMN = 60-90% of riboflavin in cells
What is the less common flavocoenzyme that riboflavin is converted into?
FAD = 5-20% of riboflavin in cells
What is the structure of Flavin mononucleotide (FMN)?
Riboflavin with an added phosphate group
What is the structure of Flavin adenine dinucleotide?
Riboflavin with a phosphate group (FMN) and an AMP
What is an AMP?
Adenosine and a monophosphate
What are the three major roles of FMN and FAD?
- Redox reactions
- Antioxidant
- Metabolism of B-vitamins
What is OIL RIG?
Oxidation is Loss
Reduction is Gain
- of electrons
Which flavocoenzyme is part of the ETC?
FMN
What part of the ETC is FMN part of?
Complex 1 - it is able to take on board the high energy electrons from the NADH, 4 hydrogen ions are being pumped into the intermembrane space
FMN is also important for some co-enzymes that metabolise…
drugs and toxins in the body
What do antioxidants protect the body from?
Free radicals - molecules with an unpaired electron so highly unstable and reactive
What do free radicals damage?
DNA, proteins and lipids
What are two FAD-dependent enzymes?
- Glutathione reductase
- Xanthine oxidase
What is the glutathione peroxidase assay?
test used to measure the activity of the enzyme glutathione peroxidase (GPx) in biological samples
What B vitamins does Riboflavin help metabolise?
Folate, B6 and niacin
How is riboflavin involved in folate metabolism?
MTHFR is an FAD-dependent enzyme which maintains the specific folate co-enzyme required to form methionine from homocysteine
How is riboflavin involved in Vitamin B6 metabolism?
Conversion of most naturally available B6 to its coenzyme form, requires the FMN dependent enzyme PPO
How is riboflavin involved in niacin metabolism?
Synthesis of niacin containing coenzymes, NAD and NADP requires a FAD-dependent enyme
What are symptoms of riboflavin deficiency?
- Redness and swelling of mouth and throat
- Cracks or sores on mouth
- Inflammation of tongue
- Dermatitis
What are the risk factors for riboflavin deficiency?
- Alcoholism
- No dairy intake
- Poorly controlled hypothyroidism
- Very physically active
What is the EAR for riboflavin?
Men = 1.1mg/day
Women = 0.9mg/day
What is the RDI for riboflavin?
Men = 1.3mg/day
Women = 1.1mg/day
What is the upper level of riboflavin intake?
No upper level of intake set
