NUTR 3210 Study Guide - Final Guide: Trigonelline, Nicotinamide, Provitamin
28 Apr 2018
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Micronutrients 3
• What’s up with Niacin (vit.B3)?
- Considered ‘anti-black-tongue- factor’
- High incidence in areas where corn is the main dietary staple (because niacin is
attached to indigestible CHO in corn ∴ poorly absorbed
- Dietary sources:
fish, meats, breads, tea, coffee (trigonelline niacin by heat from roasting)
- Animal-derived foods, vit.B3 commonly found as:
Nicotinamide NAD NADP
- In plant foods, vit.B3 predominantly found as:
Nicotinic acid (provitamin)
- Niacin can also be produced in the liver from Trp (1/60th of it)
• How does Niacin get digested and absorbed?
- Digestion of NAD + NADP required before absorption
hydrolyzed by the glycohydrolase enzyme to release free Nicotinamide
- Nicotinic acid & nicotinamide are absorbed a bit in the stomach, but most is
absorbed in the small intestine through facilitated diffusion
- In plasma, niacin found primarily as free nicotine amide, some protein bound
- Both nicotinic acid & nicotinamide can cross cell membranes by simple diffusion
in most tissues, except kidney and RBC = carrier mediated
- Both nicotinic acid & nicotinamide are precursors for NAD in the body
- Once NAD(P) is synthesized, niacin is essentially trapped within the cell.
- In their reduced form. Main functions are:
NADH
NADPH:
- CELLULAR LEVELS:
NAD+ (oxidized) NADH
NADPH (reduced) NADP+
find more resources at oneclass.com
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• How is NAD(P) produced?
- Two steps (from either NA(nicotinic acid) or TRP):
1) Convert the acid to amide
2) Build into a dinucleotide structure:
- NAD+ reduced to NADH in:
Glycolysis, TCA, B-oxidation
Role in CATABOLISM
- NADP+ reduced to NADPH in the hexose monophosphate shunt and used for:
FAs synthesis, DNA synthesis, GSH regeneration
Role in ANABOLISM
- Both NAD+ & NADP+ are 2 e- acceptors
• What are the niacin requirements/ deficiency?
- Corn/Maize
contains significant amounts, but bound ∴ not absorbed
deficient in Trp
use of lime (from limestone) can help release niacin from corn
- Deficiency leads to pellagra:
the 4 ‘D’s’ = dermatitis, dementia, diarrhea, death
- RDA recommendations include niacin produced from Trp
niacin equivalents = NE NE = mg preformed niacin + mg Trp/60
almost same dose for both sexes
• What’s up with Riboflavin (vitamin B2)?
- Sources:
Rich in foods of animal origin:
- milk/mil products, meat, etc. = sources of free riboflavin
- found in other food as FMN or FAD (bound riboflavin)
- destroyed by sunlight = milk no longer sold in glass bottles
- Absorption:
Riboflavin that is protein bound must be released before absorption = done
by HCL in the stomach
Free riboflavin absorbed by a saturable + active transport mechanism: RFT2
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find more resources at oneclass.com
• How is riboflavin transported and stored?
- Transport:
Riboflavin, FAD, FMN transported bound to protein (specially albumin)
- Storage:
Riboflavin is stored a little bit in the body in tissues like Kidney, Liver, Heart
Extra is secreted in urine
Sufficient in body to last 2-6wks when B2 is no longer consumed in diet
- FMN & FAD are mad in cells:
FMN is the primary form of riboflavin (60-95%)
Production is positively regulated by T3 hormone = increases the activity of
the flavokinase enzyme
FMN & FAD are involved in redox reactions
• How is B2 metabolized?
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
High incidence in areas where corn is the main dietary staple (because niacin is attached to indigestible cho in corn poorly absorbed. Fish, meats, breads, tea, coffee (trigonelline niacin by heat from roasting) In plant foods, vit. b3 predominantly found as: Digestion of nad + nadp required before absorption. Hydrolyzed by the glycohydrolase enzyme to release free nicotinamide. Nicotinic acid & nicotinamide are absorbed a bit in the stomach, but most is absorbed in the small intestine through facilitated diffusion. In plasma, niacin found primarily as free nicotine amide, some protein bound. Both nicotinic acid & nicotinamide can cross cell membranes by simple diffusion in most tissues, except kidney and rbc = carrier mediated. Both nicotinic acid & nicotinamide are precursors for nad in the body. Once nad(p) is synthesized, niacin is essentially trapped within the cell. Two steps (from either na(nicotinic acid) or trp): convert the acid to amide, build into a dinucleotide structure:
