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					                    BIOCHEMISTRY
            VITAMINS(WATER SOLUBLE)
 STRUCTURE FUNCTION,CLASSIFICATION,CLINICAL
                     IMPORTANCE
                LEARNING OBJECTIVE.
• At the end of lecture student should be able to know,
• Overview of water solube vitamins.
• Thiamine, sources,structure,function.
• Ribofalvin sources,structure,function.
• niacin sources,structure,function.
• Vitamin B_6 sources,structure,function.
• Folate sources,structure,function.
• Vitamin B_12 sources,structure,function.
• Pantothenic acid sources,structure,function.
• Biotin sources,structure,function.
• Vitamin C sources,structure,function.
•   OVERVIEW OF WATER-SOLUBLE VITAMINS
•   Dissolve in water
•   Generally readily excreted
•   Subject to cooking losses
•   Function as a coenzyme
•   Participate in energy metabolism
•   Susceptible to heat
•   Kidney removes and excretes excess
•   Vitamin C, thiamin and riboflavin are especially
    susceptible to heat and alkilinity
•   Hydrophilic and water will leach them from
    vegetables
• Marginal deficiency more common
•  WATER SOLUBLE VITAMINS
Thiamin        Pantothenic Acid
Riboflavin     Biotin
Niacin         Vitamin C
Vitamin B-6
Folate
Vitamin B-12

•    THIAMIN
•    Sulfur containing and nitrogen containing rings
     attached to carbon atoms
•    Part of nerve cell membranes—synthesize and
     regulate neurotransmitters
•    Functions in energy metabolism—vitamin portion of
     TPP; plays role in decarboxylation and helps form
    Acetyl Co A from pyruvate
•    DEFICIENCY
•    Heavy alcohol consumption with inadequate food
     consumption ; alcohol interferes with absorption
     (Wernicke-Korsakoff syndrome); poor and elderly at
     risk for not eating sufficient energy




•    FOOD SOURCES OF THIAMIN
•    Wide variety of food
•   White bread, pork, hot dogs, luncheon meat, cold
    cereal
•   Enriched grains/ whole grains
•   Thiaminase found in raw




    fish
•   CHEMICAL CHARACTERISTICS

•   Very labile nutrient
•   Heat
     – stable in crystalline form
     – less stable in solution
•   Alkali - very unstable with heat
     – baking soda
•   Sulfites - decomposes B-1
•   High cooking/processing losses
     – heat
     – leaching
•   DEFICIENCY OF THIAMIN
•   Occurs where rice is the only staple
•   Dry beriberi
     – Weakness, nerve degeneration, irritability, poor
       arm/leg coordination, loss of nerve




       transmission
•   Wet beriberi
     – Edema, enlarge heart, heart




       failure
•   RIBOFLAVIN
•   Coenzymes:
     – Flavin mononucleotide (FMN)
     – Flavin adenine dinucleotide (FAD)
•   Oxidation-reduction reactions
•   Electron transport chain
•   Citric Acid Cycle
•   Catabolism of fatty acids

•   FOOD SOURCES OF
    RIBOFLAVIN
•   Enriched grains
•   Liver
•   Oyster
•   Brewer’s yeast
•   Sensitive to uv radiation
    (sunlight)
•   Stored in paper, opaque
    plastic containers
•   Most plant and animal foods
•   Milk and milk drinks and yogurt supply about 15% in
    the American diet
•   Fortified cereals, bread and bread products contribute
    about 10%
•   One of four vitamins added to enriched products
•    ABSORPTION, TRANSPORT, & METABOLISM OF
     RIBOFLAVIN
•    HCL in the stomach release riboflavin from its bound
     forms
•    Absorption
       – Active or facilitated transport during low to
         moderate intake
       – Passive absorption during high intake
       – Increase with intake
•    Transported by a protein carrier in the blood
•    DEFICIENCY/TOXICITY
•    Deficiencies are rare although some people may take
     in marginal amounts
•    Drug and alcohol users and restricted caloric intake
•    Ariboflavinosis
•    Toxicity– not observed
•    FUNCTIONS OF RIBOFLAVIN
•    Accepts electrons
                                             Electron
     Transport Chain
                FAD            FADH2
    Succinate                 Fumarate
              Citric Acid Cycle
•   Participates in beta oxidation
•   FMN shuttles hydrogen ions and electrons to into the
    electron transport chain


•   RISK FOR DEFICIENCY
     – Rare
     – Low milk/dairy intake
     – Alcoholics
     – Long term phenobarbital use
•   DEFICIENCY OF RIBOFLAVIN
•   Ariboflavinosis
     – Glossitis, cheilosis, seborrheic dermatitis,
        stomatitis, eye disorder, throat disorder, nervous
        system disorder
•   Occurs within 2 months
•   Usually in combination with other




    deficiencies
•   NIACIN (NICOTINIC ACID)
•   Made from tryptophan; essential nutrient if protein
    intake is inadequate
•   60 mg tryptophan converts to 1 mg niacin
•   RDA is 14-16 NE/day for adults
•   NE include preformed and niacin derived from
    tryptophan
•   FOOD SOURCES OF NIACIN


•   Mushrooms
•   Enriched grains
•   Beef, chicken, turkey, fish
•   Heat stable; little cooking




    loss
•   ABSORPTION, TRANSPORT AND STORAGE OF
    NIACIN
•   Readily absorbed from the stomach and small intestine
•   Absorption: active transport and passive diffusion
•   Transported from the liver to all of the tissues where it
    is converted to the coenzymes
•  FUNCTIONS OF NIACIN
• NAD and NADP participates in 200+ reactions in the
   body
    2 NAD+   2NADH + H+
Glucose                          Pyruvate

    NAD+            NADH + H+
Pyruvate                               Lactate

             NAD+         NADH + H+
Isocitrate                    Alpha-ketogluterate
                      +
                NAD       NADH + H+
Alpha-ketogluterate           Succinyl CoA
              +             +
         NAD        NADH + H
Malate                         Oxaloacetate

• Electron transport chain

•   DEFICIENCY OF NIACIN
•   Pellagra
     – Occurs in 50-60 days
     – Decrease appetite & weight
•   Prevented with an adequate protein diet
     – (Untreated) corn as main staple, poor diet, Hartnup
         disease, alcoholics are at risk.




     –
•   Vitamin B-6: Pyridoxal, Pyridoxine, Pyridoxamine
•   Main coenzyme form: pyridoxal phosphate (PLP)
•   Activate enzymes needed for metabolism of CHO, fat ,
    protein
•   Transamination
•   Synthesis of hemoglobin and oxygen binding and white
    blood cells
•   Synthesis of neurotransmitters
•   FOOD SOURCES OF VITAMIN B-6
•   Meat, fish, poultry
•   Whole grains (not enriched back)
•   Banana
•   Spinach
•   Avocado
•   Potato
•   Heat and alkaline sensitive

•   ABSORPTION AND METABOLISM OF VITAMIN B-6
•   Absorbed passively
•   All three forms of B-6 are phosphorylated in the liver
•   Binds to albumin for transport in the blood
•   B-6 is stored in the liver and muscle tissue
•   Excess is excreted in urine
•   DEFICIENCY OF VITAMIN B-6
•   Microcytic hypochromic anemia
•   Seborrheic dermatitis
•   Convulsion, depression, confusion
•   Reduce immune response
•   Peripheral nerve damage
•   Who is at risk?
     – Elderly
     – Alcoholics
         •   Alcohol decreases absorption
            •   Destroy the coenzyme form
•   FOLATE (FOLIC ACID, FOLACIN)
•   Consists of pteridine group, para-aminobenzoic acid
    (PABA), and glutamic acid
•   Coenzyme form: tetrahydorfolic acid (THFA)
•   FOOD SOURCES OF FOLATE
•   Liver
•   Fortified breakfast cereals
•   Grains, legumes
•   Foliage vegetables
•   Susceptible to heat, oxidation, ultraviolet light
•   Absorption, Metabolism of Folate
•   Absorbed in the monoglutamate form with help of
    folate conjugase
•   Actively absorbed during low to moderate intake
•   Passively absorbed during high intake
•   Delivered to the liver where it is changed back to the
    polyglutamate form
•   Mostly stored in the liver
•   Excreted in the urine and bile (enterohepatic
    circulation)
•   Functions of Folate
•   DNA synthesis
     – Transfer of single carbon units
     – Synthesis of adenine and guanine
     – Anticancer drug methotrexate
•   Homocysteine metabolism
•   Neurotransmitter formation
•   Deficiency of Folate
•   Similar signs and symptoms of vitamin B-12 deficiency
•   Pregnant women
•   Alcoholics
     – Interferes with the enterohepatic circulation of
        bile/folate
•   Megaloblastic




    Anemia
•   Neural Tube Defects
•   Spina bifida
•   Anencephaly
•   Importance of folate before and during pregnancy




•
•   Toxicity of Folate
•   Epilepsy
•   Skin, respiratory disorder
•   FDA limits nonprescription supplements to 400 ug per
    tablet for non-pregnant adults
•   OTC Prenatal supplement contains 800 ug
•   Excess can mask vitamin B-12 deficiency
•   VITAMIN B-12
•  Cyanocobalamin. methlcobalamin,
5-deoxyadenosylcobalamin
•   Contains cobalt
•   Folate metabolism
•   Maintenance of the myelin sheaths
•   Rearrange 3-carbon chain fatty acids so can enter the
    Citric Acid Cycle
•   FOOD SOURCES OF
    VITAMIN B-12
•   Synthesized by bacteria,
    fungi and algae
•   (Stored primarily in the
    liver)
•   Animal products
•   Organ meat
•   Seafood
•   Eggs
•   Hot dogs
•   Milk
•   THERAPY FOR INEFFECTIVE ABSORPTION
•   Many factors can disrupt this process
•   Monthly injections of vitamin B-12
•   Vitamin B-12 nasal gel
•   Megadoses of vitamin B-12 to allow for passive
    diffusion
•   FUNCTIONS OF VITAMIN B-12
•   Helps convert methylmalonyl CoA to succinyl CoA
    (citric acid cycle)
•   RBC formation
•   Nerve functions
     – Maintains myelin sheath
•   Megalobalstic anemia

•   VITAMIN B-12 AND HOMOCYSTEINE



•   RISK FOR DEFICIENCY
•   Vegans
•   Breastfed infants of vegan moms
•   Elderly
•   Individuals with AIDS or HIV
•   DEFICIENCY OF VITAMIN B-12
•   Pernicious anemia
     – Never degeneration, weakness
     – Tingling/numbness in the extremities (parasthesia)
     – Paralysis and death
     – Looks like folate deficiency
•   Usually due to decreased absorption ability
•   Achlorhydria especially in elderly
•   Injection of B-12 needed
•   Takes ~20 years on a deficient diet to see nerve
    destruction
•   PANTOTHENIC ACID
•   Part of Coenzyme-A
•   Essential for metabolism of CHO, fat, protein

                         Glucose

Fatty acids          Acetyl-CoA          Amino Acids
                         Alcohol
• PANTOTHENIC ACID SOURCES
• Widespread in
    foods
• Organ meats
• Mushrooms
• Avacado
• Broccoli
• Whole grains

•   DEFICIENCY OF
    PANTOTHENIC ACID

•   Rare

•   Burning foot syndrome, listlessness, fatigue,
    headache, sleep disturbance, nausea, abdominal
    distress

•   Alcoholics at risk

•   Usually in combination with other deficiencies
•   BIOTIN
•   Free and bound form
•   Biocytin (protein bound form)
•   Biotinidase in small intestine

• Metabolism of CHO, fat, protein (C skeleton)
•   DNA synthesis

• BIOTIN SOURCES
• Widespread in foods
• Organ meats, fish
• Egg yolks
• Soybeans
• Whole grains
•   FUNCTIONS OF
    BIOTIN
•   Assists in the addition of CO2 to substances
•   Carboxylation of acetyl-CoA to form malonyl-CoA for
    the elongation of a fatty acid chain
•   Addition of CO2 to pyruvate to yield oxaloacetate
•   Breaks down leucine
•   Allows 3 essential amino acids to be oxidized for
    energy
•   RISK FOR DEFICIENCY
•   Rare
•   High intake of raw egg white diet
•   Alcoholics
•   Biotinidase deficiency
•   Anticonvulsant drug use
•   Signs & symptoms: skin rash, hair loss, convulsion,
    neurological disorders, impaired growth in children

•   VITAMIN C
•   Ascorbic acid (reduced form), dehydroascorbic acid
    (oxidized form)
•   Synthesized by most animals (not by human)
•   Absorbed by a specific energy dependant transport
    system
•   Passive transport if intake is high
•   Decrease absorption with high intakes
•   Excess excreted
•   FOOD SOURCES OF VITAMIN C
•   Citrus fruits
•   Potatoes
•   Green peppers
•   Cauliflower
•   Broccoli
•   Strawberries
•   Romaine lettuce
•   Spinach


•   Easily lost through cooking
•   Sensitive to heat
•   Sensitive to iron, copper, oxygen
•   VITAMIN C - ASCORBIC ACID
•   Structure
•   Metabolism
     – oxidation/reduction
     – dehydroascorbic acid
     – dehydroascorbate reductase
     – glutathione (GSH)
         • glutamate-cysteine-glycine
•   FUNCTIONS OF VITAMIN C
•   Antioxidant—donates electron minimizing free radical
    damage; Recycles oxidized vitamin E for reuse
•   Collagen synthesis
•   Stabilizes reduced form of folate enzyme
•   Enhances absorption of non-heme iron
•   Helps synthesize carnitine
•   Proper functioning of immune system
•   VITAMIN C DEFICIENCY/TOXICITY
•   Scurvy
•   Breakdown gums and joints
•   Bone pain, diarrhea, fractures, fatigue
•   UL is 2,000 mg per day
•   Can possibly enhance oxidation when consumed in
    high doses without other antioxidants
•   COLLAGEN SYNTHESIS
•
•   REFERENCES
•   Internet.
•   Essentials of medical biochemistry(Mushtaq ahmad6th
    edition)

				
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posted:10/31/2011
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