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metabolism of iodine and zinc (biochemistry)
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MINERAL METABOLISM
IODINE & ZINC
MARYAM JAMILAH BINTI ABDUL HAMID082013100002
IMS BANGALORE
INTRODUCTIONWhat is minerals metabolism?
Chemical processes undergo by minerals that occur
within a living organism in order to maintain life
IODINE
Sources:
Sea water, fish, cereals, vegetables and iodize
salt
ZINC
Sources: legumes, potato, cabbage
IODINE Biochemical function:
Formation of thyroid hormones
Thyroxine (T4)
Tri-iodothyronine (T3)
Total body contains: 25-30 mg of iodine
Normal level in blood: 5-10 mg/dL
80 % stored in the thyroid gland
Daily requirement: 150-200 µg/day
IODINE METABOLISM
GOITROGENS- Ingredients in foodstuffs, which
preventutilization of iodine
- Cassava, maize, millet, bamboo shoots, sweet potatoes and beans
THIOCYANATE- Inhibits iodine uptake by thyroid- Cabbage and tapioca
THIOUREA- Inhibits iodination of
thyroglobulin
Step 1: Uptake of IodineStep 2: Oxidation of IodineStep 3: IodinationStep 4: CouplingStep 5: StorageStep 6: UtilizationStep 7: HydrolysisStep 8: ReleaseStep 9: Salvaging of iodineStep 10:Transport of thyroid hormonesStep 11:Catabolism of thyroid hormones
Step 1: Uptake of iodine
-thyroid gland takes up
and concentrates iodine
Inhibition:
thiocyanate & perchlorate
Stimulate: TSH
Congenital defectiodine
trapping,maybe treated
by large doses of iodine
Step 2: Oxidation of iodine
-oxidized to active form
(I- I+) *can only be performed in a
thyroid
-catalyzed by thyroperoxidase
-NADPH-dependent reaction
Inhibition:
Antithyroid drugs; thiourea,
thiouracil
and methimazole
Stimulate: TSH
Congenital defectiodide oxidation
defect, treatment with T4 is
administered
Step 3: Iodination
-Thyroglobulin (Tgb) is
iodinated
-Tgb secreted by the
thyroid follicular cells
-So 3,5-di-iodotyrosin
(DIT) and 3-
monoiodotyrosine
(MIT) are produced
Step 4: Coupling Location: in the border of the follicular cells
Some of the tyrosine residues in the thyroglobulin are
aligned opposite to each other and are coupled.
When two DIT molecules couple, one molecule of
tetraiodothyronine (T4) is formed.
Tri-iodo-tyronine (T3) may be formed by de-ionization of
outer ring of T4 by 5’-deiodinase.
Under normal condition,99% is produced by T4.
Iodotyrosyl coupling defect will be treated by giving T4
DEFICIENCY of IODINE
Children
Cretinism
Adults
Goiter
Hypothyroidism
Myxedema
ZINC As a cofactor:-
Carboxypeptidase A DNA polymerase & RNA polymerase Superoxide dismutase Carbonic anhydrase
Total zinc content of body: 2g (60% in skeletal muscle, 30 % in bones)
Daily intake for adults and children: 10 mg/day
Daily intake for lactation and pregnancy: 15-20 mg/day
Highest concentration of zinc: hippocampus
area of brain and prostatic secretion
Rich dietary sources:
beans,nuts,cheese,meat and shellfish
Copper,calcium,cadmiun,iron and
phytate will interfere with absorption of
zinc.
Zinc can be used to reduce copper
absorption in Wilson’s disease
In liver, zinc is stored in combination with a
specific protein, metallothionein.
Zinc is excreted through pancreatic juice and
to a lesser extent through sweat.
Zinc stabilize insulin molecules in
pancreas
Zinc containing protein (Gusten) in saliva is
for taste sensation
Zinc dependent enzymes:
carboxypeptidase, carbonic anhydrase,
alkaline phosphatase, lactate
dehydrogenase, ethanol dehydrogenase,
glutamate dehydrogenase and superoxide
dismutase.
Zinc toxicity intake > 1000 mg/day
Inhalation of zinc oxide fumes
Rat poisons
Chronic toxicity can lead to gastric ulcer,
pancreatitis, anemia, nausea, vomiting and
pulmonary fibrosis.
Acute toxicity is manifested as fever,
excessive salivation, headache and anemia
DEFICIENCY of ZINC
Poor growth
Hypogonadism
Impaired wound healing
Reduction in number of T and B lymphocytes
Depression, dementia and other psychiatric
disorders
Impotence in male
REFERENCES
Vasudevan, D., S, S., & Vaidyanathan, K. (2013).Textbook of biochemistry for medical students.New Delhi: Jaypee Brothers Medical Publishers (P) Ltd.
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