Micronutrients (Enzyme Cofactors) Flashcards
What are the sources of biotin?
- made by intestinal bacteria (not enough tho)
- found in foods bound to proteins
How does biotin circulate in the blood?
freely, some bound to albumin
Why is there no RDA or deficiency for Biotin?
It’s very prevalent
What B vitamin is Biotin?
B7
What are the 3 key reaction involving biotin?
- pyruvate carboxylation
- malonyl CoA
- Propionate -> glucose conversion (ruminants)
What does the carboxyl group of biotin react with in an enzyme?
NH2 group of a lysine side chain
(carboxyl group then gets transferred)
What B vitamin is Folate?
B9
Where is folate found?
- folate - in food
- folic acid - in supplements and fortified foods (synthetic)
What are the three parts of folate?
Pterin ring, PABA, glutamic acid
What is the importance of folate?
- nucleic acid precursor formation
- amino acid formation
- methylation reactions
Natural folates have multiple ____ residues that must be removed for absorption (folic acid is already in this form, so no digestion required)
glutamate
Most natural folates and folic acid are converted into bioactive ____ in the intestine
5-methyltetrahydrofolate (5-methyl THF)
How is folate absorbed?
proton-coupled folate transporter (PCFT)
How is folate transported in the blood?
bound to proteins like albumin
What is the active form of folate?
5-methyl THF
What is the difference between folic acid and folate?
- folate = 1 glutamate residue
- folic acid = multiple glutamate residue
What B vitamin is Cobalamin?
B12
Cobalamin is a generic term for ____
corrinoids ; named for corrin nucleus with cobalt
Where is cobalamin found?
- made by bacteria ONLY
- animal products
- NO plant provitamin
What other micronutrient does a cobalamin deficiency affect?
folate
How is cobalamin absorbed?
- in the stomach
- binds to intrinsic factor secreted from stomach lining
- B12-IF complex goes to small intestine receptor
- complex broken down, B12 absorbed, IF released back into intestinal lumen
What are the “key players” in single carbon metabolism?
- folate (N5-methyl THF or N5,N10-methylene THF)
- Vit. B12
- S-adenosyl methionine (SAM)
In simple terms, what happens in single carbon metabolism?
methyl transfers, to eventually form dTTP that is involved in DNA synthesis and cell division, and the SAM cycle - also involved in DNA processing
The folate trap is an absence of ____ that causes ____
- vit. B12
- inhibition of the SAM cycle (arrest at N-5-methyl THF production from free folate
What is the main form of vitamin B6 in blood
pyridoxal phosphate (PLP)
Vit. B6 exists as ____ vitamers called:
- 6
- pyridoxine (plant provitamin)
- pyridoxal
- pyridoxamine
all can be phosphorylated or dephosphorylated
Vit. B6 is ____ before absorption
dephosphorylated
high levels of vit. B6 are found in ____
muscle
What B vitamin is niacin?
B3
In what form is niacin found in plants?
nicotinic acid (provitamin)
In what form is niacin found in animal-derived food
- nicotinamide
- nicotinamide adenine dinucleotide (NAD)
- nicotinamide adenine dinucleotide phosphate (NADP)
nicotinic acid and nicotinamide are precursors for ____ in the body
- NAD
- NADP
How does niacin circulate in the plasma
free nicotinamide
NAD+ reduced to NADH has a role in _____
catabolism
What has to happen to nicotinic acid before it can be converted to NAD(P)?
- converted to amide
- build into dinucleotide structure
Where is riboflavin found?
animal-derived
How is riboflavin absorbed?
- must be released from bound proteins (by HCl in stomach)
- absorbed from gut lumen by active transport: riboflavin transporter 2 (RFT2)
How are riboflavin, FAD and FMN transported in the body?
bound to proteins like albumin
production of riboflavin is positively regulated by the hormone:
T3 which increases flavokinase enzymatic activity
Order FMN, FAD and riboflavin in order of their conversion from the diet
riboflavin -> FMN -> FAD
What is riboflavin’s role in glutathione reductase?
FAD accepts electrons from NADPH and gets reduced to FADH2, then FADH2 gives its electrons to GSSG to regenerate GSH
How does thiamine exist in plants?
thiamine provitamin
how is thiamine found in animals?
in its phosphorylated form; thiamine pyrophosphate (TPP) - ACTIVE FORM
How is thiamine (TPP) found in plasma?
in free form or bound to albumin
What enzyme converts the plant provitamin version of thiamine to TPP and how?
thiamine diphosphokinase ; adds two phosphate groups
What are the two parts of TPP, which is the active site?
- carbanion -> active
- 2 phosphate groups
Which oxidative decarboxylation steps is TPP important in?
- pyruvate dehydrogenase complex
- a-ketoglutarate dehydrogenase
Where is pantothenic acid found?
EVERYWHEREEEE
What B vitamin is pantothenic acid?
B5
How is pantothenic acid found in the blood?
freely
How is pantothenic acid absorbed?
sodium-dependent multivitamin transporter (SMVT)
what is pantothenic acid a precursor for?
CoA
What are the functions of pantothenic acid?
energy metabolism ; allowing Kreb’s cycle to take place
What is the active form of pantothenic acid in fatty acid synthesis?
4-phosphopantetheine
What is the active form of pantothenic acid in oxidative reactions?
CoA
What is Beriberi caused by?
Thiamine deficiency
What is pellagra caused by?
Niacin deficiency
