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31 Cards in this Set

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What is the definition of Vitamin K?
It is a CLASS of compounds derived from napthoquinone (aka menadione) & which have antihemorrhagic activity
What are the vitamer forms and what is the difference in their structures?
1. Menadione - two ring structure w/ no side chain

2. phylloquinone (plants) - side chain w/ no double bonds "phytal" side chain

3. Menaquinone (bacteria) - side chain w/double bonds - isoprene units
Which forms are active?
The side chain must be present - menadione converted to menaquinone in liver. Then, Vit K --> KH2 for activation
What is the biochemical function of Vitamin K?
Vitamin K is a participant in the posttranslational carboxylation of glutamate (glu) to gamma-carboxyglutamate (gla)

COOH group attaches to g-carbon of glutamate.
In what classes of proteins are these reactions important? Give specific protein examples for each.
Blood Clotting Proteins - eg prothrombin and Christmas factor

Bone Matrix Proteins - eg osteocalcin
Why are gla residues important for blood clotting?
Gla residues can bind with Ca2+ causing conformational change in the protein and enabling enzymes
Describe the blood clotting mechanism and discuss how Vit K fits in
The coagulation of blood is a series of membrane-localized, cascading reactions involving modification of proteins: some of which depend on the presence of Vit K.
What is osteocalcin important for?
Bone building. Lack of vit K can result in osterperosis.
What is the Vitamin K cycle?
The cycle of activation and regeneration of Vit K.
K-->KH2-->K epoxide & back
What are the rxns/enzymes involved in the Vitamin K cycle?
K + NADPH+H--> KH2 + NADP
enzyme: Vitamin K reductase

KH2 --> Vit K epoxide
enzyme: Vit K Carboxylase
**This step Glu-->Gla!

K epoxide --> K
enzyme: Vit K epoxide reductase
KH2 is also refered to as?
Vit K hydroquinone
aka "reduced" Vitamin K
Where do the H's go in K-->KH2?
The form we eat, Vit K, is in th fully oxidizied =O's

H's attached to =O --> -OH groups
What inhibits the Vitamin K cycle? And where in the cycle?
Coumarins including warfarin and dicumarol. They are classified as anti-coagulants. Glu cannot become Gla as readily and so it inhibits blood clotting.

Specifically: epoxide reductase is inhibited
What is "special" about the carboxylase enzyme?
It is membrane bound.
What is the first step for carboxylation reactions?
The Vit K dependent protein and Vitamin K must "bind" with the carboxylase enzyme. Three binding sites: Pro-peptide binding side, Glu binding site, and Vit KH2 binding site.
After the substrates (Vit KH2 and the protein) have bound to the carboxylase enzyme, what occurs next?
Vitamin K is deprotonated by
----cys-----
|
S
group on enzyme (weak base)
(the OH nearest the side chain is the one)
After deprotonation of KH2, what then?
KH reacts with oxygen to form dioxetane which is rearranged into the epoxide/ a hydroxyl group (OH-) is release. STRONG BASE!!!
So we have a strong base formed; now what?
This strong base is able to deprotonate Glu, forming water & Glu-carbanion.

Deprotonated glu is attracted to CO2 (held in place by SECOND Cys-SH group). Gets CO2. Gla formed.
What is meant by "base amplification"?
A relatively weak base, -S is used to form a very strong base, -OH which leads to the deprotonation of Glu.
What are some vit K deficiency signs?
Hemorrhaging.
Who are most susceptible?
Elderly AND breast-fed Newborns
What is the deficiency disease in babies called?
Hemorrhagic Disease of the Newbown (HDN)
Why are newborns susceptible?
Low status; mother's milk low in Vit K
When does HDN occur, symptoms? Treatment?
HDN: 2 to 6 days after bith
intracrannial hemmorhage, GI bleeding
Treat with injections of menadione!
How is Vit K assessed?
Serum phylloquinone most common
Can also use "Protime"
What is "Protime"?
Prothrombin time. In vitro method of measuring time to clot.

Insensitive for assesment of status, but good for monitoring anti-coagulation therapy.
Food sources?
Leafy greens, liver
What are some examples of blood clotting proteins dependent on Vit K for modification?
Prothrombin and Christmas factor
What is an example of a bone matrix protein dependent on Vit K for modification?
Osteocalcin: most abundant non-collagen protein in bone matrix.

synthesized by osteoblasts; binds to hydroxyapatite; assoc. w/new bone formation.
Vitamin KH2 is called what?
Vitamin K hydroquinone.
Before the Vit K epoxide is formed by rearrangement, what is the form called (linked to the O2)?
Dioxetane