Selenium

Question 1

Organic Selenium

Answer 1

Selenomethionine (supplements, plants)
Selenocysteine (animals)
Methionine (sulfur)
Cysteine (sulfur)

Carbon bonding. Already replaced sulfur.

Question 2

Selenoproteins

Answer 2

Selenium within the structure or Se dependent proteins.

Question 3

Sources/ RDA

Answer 3

Brazil nuts
Broccoli
Garlic BEST 
Wheat
Fish (if low Mercury)

> 80% selenoamino acids (selenomethionine > selenocysteine)

50-90% selenate & selenite

Question 4

Enhancers

Answer 4

Vitamins A, C, and E.

Reduced glutathione in intestinal lumen.

Question 5

Inhibitors

Answer 5

Heavy metals, especially Mercury.

Phytic acid (via chelation and precipitation).

Question 6

Selenoprotein P

Answer 6

Forms in the liver from organic and inorganic forms of selenium.

Antioxidant and transporter.

Contains most of the body’s selenium 50-80% plasma

3 hour half life

Question 7

Glutathione peroxidase

Selenoprotein

Answer 7

Antioxidant
Protects against lipid radicals (peroxide & hydrogen-peroxide)

Spares vitamin E

Assess Se status

Transports 10-30% of Se in plasma

Question 8

Where is selenium stored?

Answer 8

Thyroid gland
Kidneys
Liver
Heart
Muscle

Question 9

Selenocysteine

Answer 9

Dietary selenocysteine cannot be used by the body.

Organic. “21st” AA. Needed for Se-dependent proteins. Has its own tRNA.

Catabolized into (inorganic) selenide.
Either methylated to be excreted via urine. Or converted back to selenocysteine (endogenous).

Question 10

Selenomethionine

Answer 10

Enters AA pool. Used for protein synthesis.
Catabolized to make selenocysteine.

Best absorbed form of all selenoproteins.

AA transporters.

Organic.

Question 11

Transport

Answer 11

Selenoamino acid are transported across basolateral membrane via AA transporters.

No one knows how inorganic selenium is transported.

Question 12

Mercury binding

Answer 12

When selenium binds to mercury, it prevents mercury from being absorbed.

Mercury can replace selenium which means selenoproteins cannot develop. Mercury poisoning.

Question 13

Inorganic Selenium

Answer 13

Selenite
Selenate
Selenide
Go directly to selenium pool and readily available.

Not incorporated into AA.

Pills, animal feed, cabbage, beets, yeast.

Question 14

Supplements

Answer 14

Either selenocysteine or an inorganic selenium is optimal.

Inorganic is directly available for use.

Selenomethionine is stored in tissues and not readily used.

Question 15

Pathway

Answer 15

1. Selenocysteine.
2. Selenide.
3. Selenoproteins.
4. Endogenous Selenocysteine.
5. Selenium dependent proteins produced.

Question 16

Hexomonophosphate shunt

Answer 16

Reduces glutathione using niacin

Question 17

Thioredoxin reductase

Answer 17

Helps reduce vitamin C and recycle it.

Question 18

Iodothyronine 5’ deiodinases

Answer 18

Helps remove iodine

Activates thyroid hormone to prevent goiter

Question 19

Antioxidant nutrient interactions

Answer 19

Se increases vit C
Vit C recycles vit E
Se spares vit E