Vitamin C Flashcards
T/F most vertebrates have a requirement for vitamin C
False, most vertebrates can make it themself
Why can’t humans create vitamin C
We are lacking one enzyme involved in its synthesis
Which enzyme do humans and primates lack for vitamin C synthesis
gulonolactone oxidase due to mutations in the gene
what is the precursor for vitamin C
UDP-glucose
Describe the absorption of vitamin C
dependent on intake
90% of intake is absorbed
Unabsorbed vitamin C is metabolized by intestinal bacteria
T/F there is a difference between synthetic and natural sources of vitamin C
false
What are vitamers
Different forms of a vitamin but both have activity
What is dehydroascorbic acid
The oxidized form of vitamin C that also has activity
It is readily reduces back to vitamin C in the ER
How is ascorbate and DHA taken up into tissues
Ascorbate- sodium-dependent transports
DHA- GLUT transporter
Ratio of ascorbate to DHA
8:1 AA to DHA
Is there a specific storage organ for vitamin C
No
adrenal and pituitary gland show the highest concentration
Describe the excretion of ascorbate
Major fate of ascorbate is excretion in urine as ascorbate or DHA
both can be filtered by kidney and reabsorbed
Does vitamin C have many metabolic actions
yes
What are the biochemical functions of ascorbate
Most characterized role is as a coenzyme in hydroxylation reactions
also plays an antioxidant role and evidence that it plays a role in regulating genes
What is collagen stabilized by
Stabilized by hydroxylations
Hydroxyproline helps stabilize the triple helix structure
what are the two AAs that are hydroxylated using ascorbate
lysine and proline
What is the enzyme used to hydroxylate proline
Proline hydroxylase
How does ascorbate help in hydroxylations
It donates electrons to hydroxylate the shit
How does ascorbic acid affect dopamine
Hydroxylates it to norepinephrine
what are the two general reactions where vitamin C acts as an oxidant
It can react with a superoxide and a proton to generate hydrogen peroxide which can be degraded by catalase
It can interact with a hydroxy radical (OH-) to produce water
How does vitamin C effect the skin
Skin is the primary barrier to pathogens and the epidermis synthesizes and secretes much collagen which contains vitamin C. Vitamin C stimulates collagen gene expression
How does vitamin C affect leukocyte function
Neutrophils and monocytes accumulate vitamin C and they protect against oxidative damage by scavenging and maintaining levels of other antioxidants, it promotes thiol-dependent signaling and gene expression pathways
What are the four ways vitamin C affects the immune system
Through the skin, leukocyte function, lymphocyte function, and inflammation
How does vitamin C affect lymphocyte function and inflammation
Lymphocyte: both B and T lymphocytes accumulate vitamin C to provide antioxidant protection and promote proliferation
Inflammation: Modules cytokines which are important to inflammation
How does vitamin C affect gene expression
Vitamin C stimulates procollagen gene transcription
Lowers expression of myelin protein gene PMP22
downregulated 31 genes
What are the three mechanisms whereby vitamin C has effects on gene expression
- Redox-dependent transcription regulation
- Increase in DNA 5-hydroxymethylcytosine content: catalyzed by proline hydroxylase, can lead to decrease or increase in gene activity
- Decreases some DNA methylation by induction of a miRNA for Dnmt3a
Vitamin C deficiency
Scurvy
takes 4-6 motnhs to appear
results from collagen synthesis deficiency
Vitamin C requirements
Vary depending on circumstances
but RDA is 50-90 mg/day
Optimum wound haling requires 20 mg/day
