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NUTR 302 > Riboflavin > Flashcards

Riboflavin Flashcards

1
Q

What are the properties of riboflavin?

A
  • From flavus = yellow and ribose=sugar
  • Yellow/orange crystal
  • Heat stable
  • Water soluble (reasonably)
  • Unstable in UV light and alkaline solutions
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2
Q

What are the active forms of riboflavin?

A
  • 2 different cofactors:
    1. FMN = flavin mononucleotide (riboflavin-5-phosphate) phosphorylated form
    2. FAD = flavin adenine dinucleotide (riboflavin-5-adenosyl-diphosphate) - gets an adenine added
    Riboflavin phosphorylated to FMN by flavokinase, FMN phosphorylated to FAD by FAD synthetase
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3
Q

What minerals are needed for riboflavin to be activated?

A
  • Zinc and Magnesium
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4
Q

What hormone is important for riboflavin and why?

A
  • Conversion of free form to FMN and FAD regulated by thyroid hormone
  • Increases flavokinase activity
  • Hypothyroidism thus causes a functional deficiency in riboflavin
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5
Q

What are the structures of riboflavin?

A
  • Riboflavin
  • FMN = Riboflavin + phosphate
  • FAD = Riboflavin + AMP
  • Some proteins use FAD and others receive FMN
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6
Q

What is riboflavins mode of action?

A
  • FMN and FAD cofactor for >100 flavoproteins
  • FMN and FAD can accept 2 H-atoms from substrate
    → important in redox reactions, dehydrogenations, hydroxylations, oxidative decarboxylations, dioxygenations
    FMN and FAD can carry hydrogens
  • Double bonds on the nitrogens that can accept hydrogens and or else give them up, goes both ways
    → reduced have gained hydrogens (extra bonds)
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7
Q

What is the metabolic role of riboflavin?

A
  • Energy production - carry reducing equivalents into the mitochondrial respiratory chain
    → TCA cycle
    → ETC
    → B-oxidation of fatty acids (much of the energy production learned about last semester riboflavin has a role in)
  • Regulation of redox status
  • Detoxification (FMOs)
  • Conversion of vitamins (B6 and folate) into their coenzyme form
  • Synthesis of niacin (B3) from tryptophan
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8
Q

How is riboflavin involved in the CAC cycle?

A
  • involved in the succinate dehydrogenase reaction, PDH reaction
  • alpha ketoglutarate use thiamin as well!
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9
Q

How is riboflavin involved in the PDH complex?

A
  • Step 4 of the PDH complex has FAD to FADH2
  • Need riboflavin to convert pyruvate to acetyl coA!
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10
Q

Why is riboflavin needed for the succinate dehydrogenase reaction?

A
  • Succinate converted to fumarate by succinate dehydrogenase using FAD cofactor
  • Oxidative reaction
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11
Q

How is riboflavin involved in the electron transport chain?

A
  • Complex 1 and 2
  • Complex 2 uses FAD and succinate dehydrogenase
  • Complex 1 uses FMNand NADH dehydrogenase module
  • Transfer of H+ which can be used to generate ATP
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12
Q

What is riboflavin’s role in beta-oxidation of fatty acids?

A
  • Involved in reduction of palmitoyl coA (fatty acid) to trans delta2 enoyl-CoA by acyl dehydrogenase
  • NAD and CoASH (Thiamin) used in later steps to convert to Acyl CoA
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13
Q

Riboflavin is also called?

A

B2

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14
Q

What are the sources of riboflavin?

A

Gut is exposed to flavins from 2 sources:
1. Diet
2. Flavins synthesized by bacteria in the large intestine
- Unknown whether this is available to host tissues (besides colonic epithelial cells)
- Synthesis increased with vegetarian diet versus meat-based diet

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15
Q

What are the riboflavin requirements?

A
  • depends on energy intake and other nutrients (including protein)
  • UL is not set because no reported cases of riboflavin toxicity
    → may be due to low solubility and prompt excretion
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16
Q

What are the populations at risk of riboflavin deficiency?

A
  • Low intake
    → Common in China, India, Africa, and Thailand: deficiency is endemic where diets lack dairy products and meat
    → Elderly
  • Pregnancy
  • Disease states:
    → Thyroid
    → Diabetes
    → Hyperbilirubinemia
17
Q

What 3 other nutrients is riboflavin deficiency associated with?

A
  1. Iron
    - Iron absorption and mobilization require reduction of Fe3+ to Fe2+
    - Flavins are most efficient reductants
  2. Vitamin B6
    - Enzyme that converts B6 to active form requires FMN
    - May also affect other kinases and phosphatases involved with B6 metabolism
  3. Folate
    - Final step in conversion of oxidized folate is catalyzed by flavin-dependent enzyme
18
Q

What are the signs and symptoms of ariboflavinosis?

A
  • Stunted growth
  • Lack of energy
  • Cheilosis and glossitis
  • Angular stomatitis
  • Skin lesions/dermatitis (seen with intakes of 0.35mg/1000kcal)
  • Corneal vascularization
  • Complicated by B6 deficiency (similar symptoms)
  • Urinary riboflavin excetion negliginle (reutilization by body)
19
Q

Explain the FAD Effect

A
  • Used to determine riboflavin status
  • EGRAC: Erythrocyte glutathione reductase activity coefficient
  • FAD Effect: If activity increases with added FAD, blood is not saturated enough with FAD
  • Values: %FAD effect (AC)
    → Adequate: <20% (1-1.20)
    → Marginal: 20-40% (1.20-1.40)
    → Deficient: >40% (>1.40)
    -Activity coefficient (AC) = +FAD/-FAD
  • % Stimulation = (AC*100)-100
  • Low glutathione reductase activity may also indicate inadequacy
20
Q

How can you determine riboflavin status?

A
  1. Urinary excretion
    - 24-hour excretion of <10% ingested may reflect inadequacy
    - Limited accuracy
  2. Serum concentration
    - Variable and indicates only current intake
  3. FAD Effect
21
Q

What are the riboflavin food sources?

A
  • Mainly in coenzyme form (>2/3 as FAD)
  • Sources:
    → Dairy and eggs (in US 1/3 of RDA)
    → Meat (liver, kidney)
    → Some green leafy vegetables
    → Enriched flour and breakfast cereals
22
Q

What is the bioavailability of riboflavin?

A
  • Related to digestibility of food (dairy and meat >plants)
  • Impaired by excess alcohol
23
Q

How is riboflavin excreted?

A
  • Little storage therefore urinary excretion of flavins reflects dietary intake
  • Excess riboflavin is rapidly excreted in urine (peak at 2 hours after ingestion)
24
Q

How is riboflavin stored?

A
  • little storage
  • Highest concentrations in liver (1/3 total body flavins, stored as FAD), kidney and heart
25
Q

How if riboflavin absorbed?

A

NUTR 302 (10 decks)

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