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25 Cards in this Set

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  • Back
What is the active form of Vitamin C?
Give the sound byte for Vitamin C.
Vit C is a reductant that participates in hydroxyalse reactions
What is a hydroxylase reaction?
One that transfers an O to a substrate (can transfer or one two O's)
What are the forms in which Vit C is found?
Ascorbic acid (all OH)
Monodehydroascorbate (one O•)
Dehydroascorbate (both =O)
In bird/mammals, what is Vit C derived from? What animals cannot make Vit c?
Cannot: humans, primates, guinea pigs, indian fruit bat
What enzyme are humans lacking in the pathway to synthesize Vit c?
Gulanolactone Oxidase
(gulanolactone -> ketogulanoloactone)
How is Vit C absorbed?
Active transport: SVCTI and SVCTII (sodium dependent Vitamin C Transporters): 80-90% depending on dose. Different transporters in diff. locations. #1: instine, liver, kidney
SVCT I absorbs what?
Ascorbic acid; low affinity for dehydroascorbate
In what form is Vit C found in blood?
How is it taken up into a cell?
Ascorbate•albumin complex (bound to proteins)
SVTC transporters absorb it in ascorbic acid form and then dehydroascorbate reductase reduces it again into ascorbate.
How is Vit C extreted?
Pee: 3 common forms, ascorbate/dehydroascorbate; one oxidized form of dehydroascorbate (diketogulonic acid) and 50% as oxalate
How does the body handle high doses of Vit C?
What is the renal threshold?
Renal thershold of 1mg/100ml - once this is exceeded, excess pours into urine
What is the main biochemical function of Vit C?
Acting as a reductant in hydroxylase reactions.
Monooxygenase and dioxygenase rxns.
What are two important monooxygenase reactions?
Dopamine --> Norephinephrine
a-amidation reactions that activate peptide hormones/ hormone releasing factors. Some include CCK, calcitonin, gastrin, vasopressin.

NOTE!!! Ascorbate only participates in ONE (1st?) step of reaction
Besides Vit C, what is required for monooxygenase reactions?

What about for dioxygenase reactions?
Mono: Cu and O2

Di: Fe and a-ketoglutarate and O2
What form does Vit C participate in monooxygenase reactions?

What is its role?

It reduces Cu again (enzyme of rxn is Cu dependent)
Ascorbate -> monodehydroascorbate
Name the two enzymes that participate in monooxygenase reactions
dopamine b-hydroxylase
peptidyl glycine hydroxylase
What do a-amidation reactions do?
1st stage in overall reaction that activates peptide hormones (CCK, gastrin, calcitonin) & hormone releasing factors by replacing COOH end with NH2.
Enzyme for a-amidation reaction?
Peptidyl glycine hydroxylase

(at least remember hydroxylase)
What are two examples of dioxygenase reactions?
Prolyl and Lysyl hydroxylases
In general, these reactions are involved in stabilizing collagen and pro-collagen, for example.
Why is ascorbate not used stoicheometrically in dioxygenase reactions?
Because it reduces only the ferrous form of iron, which doesn't always get produced
What are signs of Vit C deficiency?
Capillary fragility due to high histidine levels - hemmoraging
Impaired wound healing
Weakening of collagenous structures in bones, teeth
pithed frog
How quickly can sign of Vit C deficiency appear?
45-80 days
Assesment of Vit C levels?
No functional test; plasma ascorbate measured
Vit C in foods? Losses?
Citrus fruits, leafy greens.

Oxidation during storage and losses during cooking (via H20)
Why is hemorrhaging common with Vit C def?
Because the breakdown of histadine requires Vit C. High levels of histidine cause capillary fragility.