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27 Cards in this Set
- Front
- Back
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Where is Zinc found in the body? |
Highest concentration in bone, prostate, skin, retina Content in body 1.5- 2.5 g |
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Sources in food |
Protein-rich diets tend to be high in Zn
Red meats, seafood, poultry, pork, dairy (high in protein foods) Americans get ~70% of dietary zinc from animal sources Whole grains, vegetables (less absorption due tophytates) |
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Factors that decrease absorption |
Phytic acid
Oxalic acid Divalent minerals (Calcium, iron) may reduce absorption Polyphenols (in tea and coffee) |
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Digestion |
Normally bound to PRO so needs to be hydrolyzed |
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Absorption |
Passive diffusion & carrier-mediated transport
Carrier-mediated: Predominant: Zip4 transporter Divalent mineral transporter 1 (DMT1) Bind to AA-- Amino acid transporters? Paracellular diffusion When Zn intake exceed capacity of Zip4 Absorption varies generally from 10-60% Increases with low intake and decreases with high intake Helps maintain Zn homeostasis in the body |
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Enterocyte zinc use |
Used functionally or stored bound to proteins Metallothioenine- short-term Zn storage Main zn storage protin Transported across basolateral membrane into plasma (Zinc transporters ZnT) |
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How is Zinc transported in the blood |
Transport in blood
Bound to albumin (primary, ~60%) macroglobulin and IgG Amino Acids– histidine and cysteine |
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Where is zinc taken after blood transport |
To liver |
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Uptake of Zinc |
ZIPs and ZnTs facilitate Zn uptake and release butunclear (many of these transporters throughout thebody)
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How Zinc regulates Metallothionein |
Serves to store Zn but also may transport it toenzymes
Also exhibits antioxidant-type function =With stress synthesis increased, helps control free radical concentrations (acute phase response) Zinc can be released from metallothionein bylysosomal proteases |
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Metallothionein |
Zinc regulates the gene expression of thioneinby binding metal regulatory elements (MREs)found in the promotor region of thionein gene ¨
A Zn-dependent metal transcription factor(MTF) binds promotor region to inducesynthesis Thus zinc directly regulates production to trapzinc Will trap other minerals too, esp copper (highzinc may induce a copper deficiency) |
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Zinc Function |
Catalytic role
Structural role Regulatory role |
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Catalytic role of Zinc |
metalloenzymes
>300 known Zn-dependent enzymes DNA/RNA polymerase Enzymes involved in fatty acid, carbohydrate andprotein metabolism |
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Structural roll of Zinc |
Stabilizes proteins and membrane structure |
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Regulatory role of Zinc |
Control gene transcription, stabilizes transcription factors to bind DNA = zinc fingers |
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Zinc Fingers |
Many transcription factors contain zinc
Conformational change so that it resembles a “finger” when bound to zinc Interact with metal response elements (MREs) Nearly 2000 zinc-dependent transcription factors identified |
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Immune Defense |
Thymulin= Zn-dependent hormone peptide Binds T-cells and promotes differentiation andfunction
Zn deficiency decreases thymulin= T-cellnumbers and function May increase susceptibility to illness
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Antioxidant function |
Protects from oxidation: Used in sunscreens, prevents oxidation of metal (rust)
Cu-Zn SOD Stabilizes proteins and lipids by keeping them in reduced state Metallothionein : Scavenges free radicals with cysteine |
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Other Zinc roles |
Enzymes for heme synthesis
Collagen synthesis (wound repair) Alcohol detoxification Metabolism of vitamin A (retinol binding proteins) Hormone release (insulin) |
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Interaction with Vitamin A |
(formation of retinaldehyde from retinol– Zn-dependent dehydrogenase, Znalso needed for synthesis of retinol bindingprotein for retinol mobilization)
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Interaction with Copper |
Copper– Zn adversely affects copper absorption attributed to zincs stimulation ofmetallothionein which has a higher affinityfor copper than zinc
Increased concentrations of metallothionein bind and “trap” copper in the enterocyte Risk of copper deficiency set the UL for zincat 40 mg/day |
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Excretion of Zinc |
Mostly through GI tract-- feces
Sloughing of intestinal cells, pancreatic secretions Small amount in urine skin exfoliation/sweat |
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RDA |
Men 11 mg women 8 mg |
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Deficiency |
Impaired growth and development
Skin lesions Night blindness Impaired reproduction Delayed wound healing Impaired immune function |
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Those at risk for deficiency |
Elderly, decreased absorption/eat less meat
Vegetarians– may need 50% more in diet due to high phytates Needs increased by alcoholism, chronic illness,stress, trauama, surgery, malabsorption |
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how is zinc toxic |
relatively nontoxic
UL = 40 mg Toxicity associated with zinc’s influence on copper |
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Assessment of zinc |
Zinc in RBCs, leukocytes, neutrophils, plasma/ serum
Metallothionein concentrations Urinary or hair zinc Activity of zinc-dependent enzymes But really there is no robust, sensitive marker for Zn Why? ú Homeostatic mechanisms, Non-specific deficiency symptoms |
