Zinc (Part 2) Flashcards
What are the functions of zinc?
Catalytic, structural, regulatory
What is carbonic anhydrase?
First characterized zinc metalloenzyme
What does carbonic anhydrase do?
Interconverts carbon dioxide and bicarbonate to maintain acid-base balance in blood
What is the rxn of carbonic anhydrase?
CO2 +H20 -> H2CO3 (bicarbonate)
In carbonic anhydrase, zinc is coordinated by what?
3 histidine residues
What are examples of Zn catalytic functions?
Metalloenzymes:
- Alcohol dehydrogenase
- RNA polymerase
- Alkaline phosphatase
- carbonic anhydrase
- carboxypeptidase A
What is carboxypeptidase?
A digestive enzyme produced by the pancreas
What does carboxypeptidase do?
Hydrolyzes peptide bonds
In carboxypeptidase, zinc is coordinated by what?
2 histidine and 1 glutamic acid residue
For carboxypeptidase, the R’ group can be any AA except?
Arg, Pro, Lys, and hydroxyproline
Why does the pancreas cause the body to lose a lot of zinc?
Because these digestive enzymes are secreted from the pancreas and a lot of them contain zinc.
What is an example of a structural zinc function?
Zn binding proteins
What is an example of a zinc binding protein?
Superoxide Dismutase 1
What is superoxide dismutase 1?
An antioxidant enzyme
What does Superoxide Dismutase 1 do?
It catalyzes the “dismutation” of superoxide, converting it to hydrogen peroxide
What is the role of Cu in superoxide dismutase 1?
Serves a catalytic role in electron transfer during dismutation rxn
What is the role of Zn in superoxide dismutase 1?
Serves a structural role
What is the most common DNA binding domain?
Zinc finger domain
What are two different forms of mammalian zinc fingers?
C4 (4 Cysteine residues): Nuclear receptors and C2H2 (2 Cysteine and 2 Histidine residues) family
What are examples of C4: Nuclear receptors?
Retinoic Acid Receptor (RAR) and Vitamin D receptor (VDR)
Why do proteins have zinc finger domains?
It allows proteins to bind to DNA which may activate or inhibit the expression of genes.
Zinc Status assessment
Plasma zinc <70micrograms/dL
Why is Plasma Zn not a very good indicator?
Because it is affected by many factors such as stress, meal, time of the day, infection, medications
What is an example of genetic zn deficiency?
AE (Acrodermatitis enteropathica)
Who was the first person to document Zn deficiency?
Ananda Prasad
When was Zn declared to be an essential nutrient in the U.S.?
1974
Why is the skin on the cheeks affected by AE so much?
Because the skin on the cheeks is one of the fastest turning over pieces of skin on your face and have the highest zinc demand.
Where is Zn deficiency prevalence high?
Africa, Asia
Loss of life of children under the age of 5 is due to?
Vit. A def, Zn def, and Iron def.
Vitamin A and Zn account for how much of childhood disability-adjusted-life-years
9%
What is the RDA for Zn?
~10 mg
Zn toxcity
Does not exist because body can excrete excess zinc
Symptoms of toxicity can exist if
200 mg of zinc is taken
What are the symptoms of Zn toxicity?
Nausea, vomiting, epigastric pain, abdominal cramps, bloody diarrhea
Chronic ingestion of Zn (~40 mg/day) can cause what?
Cu def
Penny case: why were his zn levels high?
Because he ingested post 1982 pennies which are mainly made of zinc and they were partially digested causing increase in zinc levels
