Riboflavin/Vitamin B2

Question 1

• Riboflavin forms two co-enzyme derivatives
  1. ____ ________ (FMN)
  2. ____ ______ _________ (FAD)

Answer 1

• Flavin Mononucleotide
• Flavin Adenine Dinucleotide

Question 2

Riboflavin Digestion, Absorption & Transport
* Riboflavin in food can be free, bound to protein or
within its FMN or FAD _____ ______
Stomach
* Riboflavin attached to protein is freed by _______ _______
& ___ ____
Small Intestine
* Further breakdown by _______ _____
* ___ converted to ____ then free _____
* Absorbed by a _______, __ dependent carrier system
* Absorbed by _______ at high doses
Plasma
* Taken to liver by ______ _____. Converted to FMN or FAD
* Free riboflavin, FMN and FAD are found in the plasma
bound to ________

Answer 2

• free, co-enzyme derivatives
• gastric enzymes, HCL acid
• intestinal enzymes
• FAD, FMN, riboflavin
• saturable, Na
• diffusion
• portal vein
• proteins

Question 3

Riboflavin Storage
* Free riboflavin crosses cell wall by _____ _______
process except in the ____ where FAD is taken up
* Highest [ ] of riboflavin is in the _____,______ and _____
* Stores sufficient for - weeks
* Usually converted to ___ or ___ once in cells – under
______ control
* Primarily excreted as ____ riboflavin in the ______ – bright
yellow
* Reflects _____ intake

Answer 3

• carrier mediated, brain
• liver, kidneys and heart
• 2-6
• FAD, FMN, hormonal
• free, urine
• dietary

Question 4

Riboflavin Functions – Summary:
FMN and FAD function as _______ _____ for _______
_______ are enzymes involved in _______ _______ reactions
* _______ in the metabolism of _______ and energy
* Role in activation of vitamin ___
* Role in conversion of ________ to niacin
* Role in ____ metabolism

Answer 4

• prosthetic groups, flavoproteins
• Flavoproteins, oxidation reduction
• Coenzymes, macronutrients
• B6
• tryptophan
• folate

Question 5

Riboflavin - Functions
FMN/ FAD
* Cofactors for a wide variety of oxidative enzyme systems (>100)
* Reversible H transfer in oxidation-reduction reactions
* Accept a pair of H atoms (with their electrons) to form FMNH2 or FADH2
* Flavin ring is reduced by electron transfers
* Therefore, able to be carrier for hydrogen ions and electrons and
contribute to various oxidation/reduction reactions
Roles Include
* Participate in flavoproteins in the oxidation (electron transport) chain
* Cofactors for enzymes required for reactions in the TCA cycle
* Cofactor for enzymes used in fatty acid oxidation
* Cofactor for enzymes which activate vitamin B6
* Used in the synthesis of the active form of folate

Question 6

Riboflavin Deficiency - ________
* ______ ______ – inflammation/ cracking at angles of mouth
* _____ – cracking of lips
* ______ – inflammation/ swelling of tongue
* _______ – red or blood mouth cavity
* ______ – swollen mouth cavity
* _______ ______ - Itchy scaly skin, rash
* _______ – peripheral nerve dysfunction
* Riboflavin deficiency rarely occurs in _______ (other deficiencies often
co-exist). It is rare in Australia.
* People with excess ______ intake are at risk

Answer 6

• Ariboflavinosis
• Angular stomatitis
• Cheilosis
• Glossitis
• Hyperaemia
• Oedema
• Sebhorrheic dermatitis
• Neuropathy
• isolation
• alcohol

Question 7

Riboflavin Toxicity
__ toxicity reported – large oral doses appear _____
* excess dietary intake is readily excreted in ______
* ______ body stores
* no reported _____ of high intakes

Answer 7

• no, safe
• urine
• limited
• benefits

Question 8

Riboflavin in Food
Destroyed by exposure to UV – __ hours exposure depletes Riboflavin by __%
High (>1 mg/100g):
* yeast extract (vegemite) (22)
* liver (4)
* fortified breakfast cereals (1-2)
Medium (0.1 – 1 mg/100g)
* dairy e.g. cheese (0.5), yoghurt (0.4), milk (0.2)
* egg (0.4), meat (0.3)
* bran eg wheat bran (0.26)
* bread (wholemeal/ white) (0.12/ 0.07)
Low (<0.1 mg/100g)
* fruit, vegetables

Answer 8

• 4
• 70

Question 9

Assessment of Riboflavin Status
* Measurement of activity of _______- ________ ______ (FAD dependent enzyme)
* Measurement of activity of _________ ________ ________ (FMN dependent
enzyme)
* _____ riboflavin concentrations
* Urinary riboflavin excretion/g ______

Answer 9

• erythrocyte glutathione reductase
• pyridoxamine phosphate oxidase
• Cellular
• creatinine