Ascorbic Acid Flashcards
Why can humans not synthesize ascorbic acid
lack gluconolactone oxidase (last enzymatic step)
Vitamin C sources
citrus, papaya, cantaloupe, broccoli, bell peppers, strawberries
How is Vit C absorbed
active transport
What must occur before Vit C is absorbed
it has to be oxidized to dehyrdoascorbate
What occurs to dehydroascorbate in enterocytes
reduction to ascorbic acid (dehydroascorbate reductase, requires reduced GSH)
Where does absorption occur
primarily in distal portion of SI
Is it better to have high intakes or low intakes of Vit C at a time
Low due to better absorption; 98% at low, 16% at high
What are potential factors that can impair absorption
pectin, zinc, high iron content in GI (AA descruction)
Absorption method for Vit C
sodium-independent carrier-mediated transport
How does Vit.C transport in plasma
free form, moves freely into cells
tissue and plasma level reflect intake until ~Xmg/day
90
Explain the antioxidant mechanism
reducing agent
Reactive oxygen species: OH*, O2-, H2O2, HO2
Purpose: oxidize LDL and red blood cells
Explain pro-oxidant mechanism
reacts with free Fe+3 or Cu+1
Explain collagen transormation
Fe+2 required to hydroxylate proline to aggregate collagen molecule–> ascorbate reduces iron back to ferrous state
Collagen transformation mechanism
Vit C required for hydroxylation of lysine residues –>permit cross-linking of collagen and other post-translational modifications
