Transcript B vitamins

PHM142 Fall 2016
Instructor: Dr. Jeffrey Henderson
Vitamin B
October 4th, 2016
Presentation by: Vicky Wong, Tiffany Wu, Selina Pang, Hiu Yan Fiona Ho
What is Vitamin B (B Complex)?
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Water soluble vitamins
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Need continuous daily supply
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Play crucial role in cell metabolism
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Form part of coenzymes that help enzymes release
energy from foods
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Found in grains, meat, poultry, eggs, fish, milk, vegetables
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Vitamin B1, B2, B3, B5, B6, B7, B9, B12
Vitamin B1 (Thiamine)
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Whole-grain, enriched grain products, pork
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Increase need with increasing body weight and
metabolism
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No toxicity observed
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Synthesize coenzyme thiamine pyrophosphate (TPP)
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Deficiency causes a disease called beriberi
Thiamine Pyrophosphate (TPP)
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Coenzyme
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Synthesized from thiamine using ATP
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Reactive group: thiazolium ring
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Pyruvate decarboxylase
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Catalyzes reaction for alcohol fermentation
Pyruvate dehydrogenase
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Complex converts pyruvate to acetyl CoA for
Krebs cycle
B1 Deficiency (Beriberi)
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•
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“Dry” symptoms
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Damage to nervous system
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Ex. Weakness in legs, atrophy of
muscles and skin
“Wet” symptoms
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Damage to cardiovascular system
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Ex. increased blood pressure, edema,
enlarged heart
Other symptoms
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Anorexia, nausea
Causes of B1 Deficiency
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Infections or increasing physical exertion
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Fever
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Pregnancy
Alcoholism
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Impairs B1 absorption and enhances excretion
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Wernicke-Korsakoff syndrome (brain damage)
Gastrointestinal disturbances
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Vomiting, gastric bypass
Vitamin B2 (Riboflavin)
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Precursor of two important coenzymes,
Flavin Adenine Dinucleotide (FAD) and
Flavin Mononucleotide (FMN)
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They have several functions:
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Electron carriers → important in metabolic
pathways involving carbohydrates, fats,
and proteins
Antioxidant
Involved in the metabolism of other B
vitamins (such as B3 and B6)
Ex. Role of FAD and FMN in Krebs Cycle & ETC
Ex. Antioxidant Effects of Riboflavin
Vitamin B2 (Riboflavin)
• Dietary source: dairy products, dark green vegetables, whole grain, meat
• Deficiency symptoms: sore throat, inflammation of tongue, lesions of the skin
• Deficiency may impair iron absorption and hemoglobin synthesis
• No known toxicity
Vitamin B3 (Niacin / Nicotinic Acid)
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Dietary Sources: meat, fish, and grain products
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Deficiency: severe deficiency causes pellagra
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Toxicity: high doses of niacin can be toxic
Vitamin B3 (Niacin / Nicotinic Acid)
• Derivative: Nicotinamide
• Precursors of the coenzymes:
nicotinamide adenine dinucleotide
(NAD) and nicotinamide adenine
dinucleotide phosphate (NADP)
NAD & NADP
• Redox Reactions:
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Accept or donate electrons
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NAD
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Degrade carbohydrates, fats, proteins and alcohol
NADP
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Synthesize fatty acids, cholesterol
• Non-Redox Reactions:
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NAD
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Separate the Nicotinamide moiety from NAD
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Transfer ADP-ribose to acceptors.
NAD & NADP Metabolic Pathway
Vitamin B3 Deficiency
• Symptoms of Mild Deficiency:
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Indigestion, fatigue, canker sores, vomiting, poor circulation, depression
• Symptoms of Severe Deficiency: Pellagra
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Characterized by the 4 D's:
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Dermatitis
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Diarrhea
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Dementia
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Death
Vitamin B5 (Pantothenic acid)
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In beef, poultry, whole grains, potatoes, tomatoes, and broccoli
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Deficiency rare
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Symptoms: failure of body systems, fatigue, neurological
disturbances etc.
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No toxic effects observed
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Most exist as CoA or acyl carrier protein (ACP)
Coenzyme A (CoA)
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Synthesized from vitamin B5
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Carrier of acetyl and other acyl groups
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Ex. Acetyl CoA used in Krebs cycle
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Energy metabolism
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Oxidation of fatty acids
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Lipid metabolism
CoA Synthesis
from Pantothenic
Acid
Other Possible Functions
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Skin moisturization
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Improve symptoms of rheumatoid arthritis
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Pantotheine (derivative of pantothenate) can help reduce fats
for high cholesterol people
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Helps body use riboflavin (vitamin B2)
Side Note:
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Destroyed by canning, freezing, and refining processes
Vitamin B6
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Sources: pork, meats, whole grains
and cereals, fruits, vegetables
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Deficiency symptoms:
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Skin disorders, cracks at corners of mouth, anemia, kidney
stones, nausea, mental confusion in infants
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Toxicity symptoms:
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Neurological damage
Vitamin B6
• 3 forms - pyridoxal, pyridoxine, pyridoxamine
• Active coenzyme form is pyridoxal-5-phosphate, PLP
(two tautomeric forms)
Pyridoxal-5-Phosphate (PLP)
● Transfer amino groups -NH2from amino acids to keto acids
● Involved in 100+ reactions, mainly in amino acid and
neurotransmitter metabolism
○ Transaminations, α- and β-decarboxylations, β- and γ-eliminations,
racemizations, aldol reactions
○ Protein and urea metabolism
○ Conversion from tryptophan to niacin or to serotonin
○ Synthesis of heme, insulin, nucleic acids, lecithin (phospholipid)
7 Classes of Reactions Catalyzed by PLP
Chemistry of PLP
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Versatile
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Reacts with amino groups on amino
acids to form stable Schiff base
(aldimine) adducts
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Stabilizes reaction intermediates by
acting as an electron sink
Vitamin B9 (Folate/Folic Acid)
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Folate is the natural form, folic acid
is the synthetic form
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Dietary source: lentils, beans, dark
green vegetables
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In Canada, folic acid is added into
white flour to reduce the risk of
neural tube defects
Vitamin B9 (Folate/Folic Acid)
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Primary coenzyme form is THF (tetrahydrofolate)
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Methyl donor in many reactions
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Functions:
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Synthesizing DNA and RNA
Converts vitamin B12 to coenzyme form
EX. THF in conversion of dUMP to dTMP
Folate Deficiency
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Low levels of folate in early pregnancy
may cause neural tube defects in the
fetus
• Brain and spinal cord
• Open or closed defect
• Anencephaly, spina bifida, early
death, etc.
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Deficiency in folate may lead to anemia
• Need folate to make RBC
Summary
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B Vitamins are water soluble and play a crucial role in cell metabolisms as they form part of coenzymes that help enzymes release energy from foods.
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Vitamin B1 (Thiamine) synthesizes coenzyme thiamine pyrophosphate (TPP), with an active thiazolium ring, which enables the enzyme pyruvate dehydrogenase
to convert pyruvate to acetyl-CoA in the Krebs cycle. Thiamine deficiency causes a disease called beriberi, which has “wet” (cardiovascular) and “dry” (nervous
system) symptoms.
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Vitamin B2 (riboflavin) forms two coenzymes, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). These coenzymes are involved in energy
metabolism (carbohydrate, fat, protein) as electron carriers. They also have antioxidant effects through FAD-dependent glutathione reductase.
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Vitamin B3 (Niacin) is the precursor of the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). Niacin
coenzymes degrade carbohydrates, fats, proteins and alcohols and synthesize fatty acids and cholesterol. They play a role in cell signaling and DNA repair.
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Vitamin B5 (Pantothenic acid) is part of the chemical structure for coenzyme A (CoA), which is a carrier of acetyl and acyl groups used in many metabolic
pathways including the Krebs cycle.
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Vitamin B6’s active form is pyridoxal-5-phosphate (PLP), which is very versatile and participates in many reactions, mainly in amino acid and neurotransmitter
metabolism.
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Vitamin B9 (folic acid/folate) is a precursor for tetrahydrofolate (THF), which is an important methyl donor in many reactions. THF is involved in DNA and RNA
synthesis so it is crucial to rapidly dividing cells. Deficiency in folate can cause anemia (there will be large but few RBC) and neural tube defect in developing fetus.
References
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http://extension.colostate.edu/docs/pubs/foodnut/09312.pdf
Brown, G. M. (1958, September 15). The mechanism of pantothenic acid. The Journal Of Biological Chemistry, 234(2).
Cowgill, G. R. (1938, September 10). HUMAN REQUIREMENTS FOR VITAMIN B1. The Journal of American Medical Association, 11(111),
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