Vitamins Trumbly Flashcards
Vitamins
-Vitamins (Definition): ORGANIC molecules required in
the diet in small quantities.
- Classified as water soluble (B’s, C) and fat soluble (A, D, E, K)
* This affects absorption, transport, and storage - Many first identified by deficiencies in certain populations
- Deficiencies in this country are now rare except for special circumstances
- Folates and B12 already presented in separate lecture
Vitamin B1 (Thiamin)
-It has vitamin form (Thiamin) in normal diet/supplements, carbanion intermediate serving in part of catalytic mechanism, and then the coenzyme (functional) form in the body which is “thiamin diphosphate”.
-This vitamin is part of the coenzyme TPP (thiamin pyrophosphate) = oxidative decarboxylation reactions in energy metabolism:
*Pyruvate dehydrogenase
*alpha-ketoglutarate dehydrogenase
*Branched-chain keto-acid dehydrogenase
(isoleucine, leucine, valine)
- Good food sources of Vitamin B1 (Thiamin):
* meat and fish
* whole grain and enriched grains
* legumes - Diseases of B1 Deficiency:
* Beriberi “I can’t, I can’t”
- Wet beriberi with edema
- Dry beriberi with muscle wasting
* Dry is common in Asia (milled rice diet)
* Beriberi symptoms: weakness, paralysis, wasting away. (disrupts CHO metabolism)*Neurological problems from severe alcoholism: Wernicke's encephalopathy and Korsakoff's psychosis
-Thiamin and Alcohol
*Impairs absorption of thiamin
*Enhances thiamin excretion by kidneys
*Displaces more nutrient dense food in diet
(because alcoholics drink alcohol and eat less)
*4 0ut of 5 alcoholics are deficient in thiamin!
Riboflavin (Vitamin B2)
-The Vitamin form is Riboflavin (it is a reduced form of Ribose). The name Riboflavin means that it has a bright yellow color
- Riboflavin has TWO COENZYME forms:
1) FMN (just phosphorylated form of vitamin)
2) FAD (the FMN combines with ADP)
-Flavin coenzymes:
*Energy metabolism
*Redox reactions
*Beta-oxidation
*Converts vitamin A and folate to active forms,
also converts tryptophan to niacin (so it is
required in metabolism of several other vitamins)
*It is needed for Formation of vitamins B6 and K
Best food sources:
-Milk, grains, green vegetables, meats
Riboflavin is easily destroyed by ultraviolet light (because the ring structures, just like with DNA, can absorb/are sensitive to UV light), so this is why you sometimes see “opaque containers for milk” to protect it from being degraded.
Riboflavin deficiency
- "Ariboflavinosis
* Sore throat
* Cheilosis (fissures at corner of mouth)
* Glossitis (swollen and inflamed tongue)
- Rare and is usually only seen in ALCOHOLICS or when accompanied by other nutrient deficiencies
NIacin (B3)
- There are TWO vitamin forms
1) Nicotinic acid
2) Nicotinamide - TWO coenzyme forms as well:
1) “NAD” (Nicotinamide Adenine Dinucleotide).
2) If the NAD structure has a phosphate group (phosphorylation site) at the 2’ hydroxyl (OH) region, it will be the second coenzyme = “NADP”
Summary Niacin:
-Vitamin forms : nicotinic acid and nicotinamide
-***Can be made in the body from TRYPTOPHAN
(but this is not an efficient process so it’s better to get it from the diet)
-Coenzyme forms: NADH and NADPH
*NADH: OXIDIZED by respiratory chain to form
ATP
*NADPH: REDUCTANT (source of reducing
power) in biosynthetic reactions
-Other functions:
*Synthesis of fatty acids, cholesterol, steroid
hormones, and DNA (cofactor/NADPH for
ribonucleotide reductase)
*Metabolizes Vitamin C and folate (so needed
for metabolism of these two other vitamins)
Good Food Sources of Niacin (B3):
*Protein rich foods - like lean meats and peanut
butter; enriched grains, some vegetables
Also can be made by tryptophan (60mg tryptophan is needed for 1mg niacin, so this is not very efficient)
- **NIACIN DEFICIENCY = “Pellegra”
- Symptroms: “4 D’s” = dermatitis, dementia, diarrhea, death
- Common in areas with poor nutrition
- Also food in Hartnup’s disease, due to genetic defect in tryptophan uptake - Niacin TOXICITY
- Niacin Flush is only seen with supplementation of nicotinic acid (not nicotinamide) at about 1g/day
- Supplemental niacin can lead to skin inflammation and flushing, heart burn, nausea, increased plasma glucose and liver damage.
Why do people take large amounts of Niacin?
- Can lower LDL cholesterol, lower triglycerides and increase HDL cholesterol (so niacin appeared to have positive effects for treating dyslipidemia). The following are brand names for niacin pills/drugs:
- Niaspan
- Niacor
- Slo-Niacin
- However, NIH ended a niacin study 18 months early because there was no evidence that niacin reduced risk of cardiovascular events
- Patients did see increase in HDL and decrease in triglyceride levels (but it didn’t seem to improve cardiovascular health)
- Additionally, many patients have difficulty tolerating niacin.
Pantothenic acid (Vitamin B5)
- Vitamin form is “pantothenic acid”
- Coenzyme form is “Coenzyme A” = “CoASH” (This coenzyme has ADP as part of it’s structure which is attached to the pantothenic acid, just like many other vitamin coenzymes have ADP attached)
Pantothenic Acid
- Use of glucose, amino acids, and fatty acids for ATP production
- Synthesize:
- Heme
* Cholesterol - Bile salts
- Phospholipids
- Fatty acids
- Steroid hormones
- Heme
*Deficency is NOT WELL KNOWN, since pantothenic acid is found in most foods, and is also synthesized by intestinal bacteria.
Vitamin B6
***Interconversion of vitamin B6 forms:
(The simple forms on left side are possible vitamin forms, and the forms on right have phosphate group added making some of them the coenzyme forms)
- “Peridoxine” is the MOST COMMON Vitamin form of B6 (in vitamin supplements)
- It gets metabolized in body by “Kinase Phosphatase” to become “Peridoxine Phosphate” and then is turned by enzyme “Oxidase” into “Peridoxal phosphate”
- “Peridoxal” is another vitamin form and gets interconverted (back and forth) to the same product “Pyridoxal phosphate” as before by the same enzyme “Kinase Phosphatase” (but this time there is no second “Oxidase” enzyme step required to form the product)
- “Pyridoxal phosphate” product can then be interconverted/back and forth by “Aminotransferases” to “pyridoxamine phosphate”
- (The “Pyridoxamine phosphate” can also go in a one-way reaction back to the “Pyridoxal phosphate” by the enzyme “Oxidase”)
- A Third vitamin form “Pyridoxamine” can also make “Pyridoxamine phosphate” (and go back and forth) by using the enzyme “Kinase Phosphatase”
- My summary:
- All of these vitamin forms can be converted to “Pyridoxal” vitamin and “Pyridoxamine” vitamin, but you can’t make “Pyridoxine” from anything other than the pyrodixine phosphate (this is not a coenzyme).
- “Pyridoxal phsophate” and “Pyridoxamine phosphate are the two coenzymes” of B6
- “Pyridoxine, Pyridoxal, and Pyridoxamine” are the three vitamin forms of B6. The top form/pyridoxine is the most common vitamin form (and that’s probably why it can be converted to the others in one way forward direction but you can’t make it from the others).
- Vitamin B6 Trumbly Slide:
- Different forms may be interconverted - and it is stored in muscle and liver
- Coenzymes: pyrodixal phosphate (PLP) and pyridoxamine phosphate (PMP)
- amino acid metabolism, especially transamination and decarboxylation
- Fatty acid metabolism
- Needed for conversion of tryptophan to niacin and serotonin (So B6 is needed to make niacin and seratonin from tryptophan / it converts tryptophan into niacin and seratonin…. so a deficiency of B6 can exacerbate a niacin deficiency by not allowing you to make niacin in the body).
- B6 Sources: most foods
- DEFICIENCY OF B6 IS RARE, because it is found in most foods
- “Isoniazid”, also known as “isonicotinylhydrazine”(or INH) = B6 ANTAGONIST that is used to treat TUBERCULOSIS
- When INH is used, B6 Supplements are given!
B6 TOXICITY (overdose)
- Has been used to treat premenstrual syndrome, carpel tunnel syndrome, and sleep disorders
- Taken at high doses (2g/day) can cause NEUROLOGICAL problems = difficulty in walking and numbness of hands and feet
Biotin (B7)
Vitamin form is Biotin (B7)
The Biotin Vitamin form is used as a coenzyme by FORMING COVALENT links/bonds to LYSINE residue on the enzyme that it is working with. Here are two examples;
1) Biotinyl-lysine (biocytin) ….it is attached to the lysine group serving as a coenzyme.
2) Carboxy-biocytin …..this is the same as one, but it has carboxy (COO-) group on it’s terminal instead of acid (COOH) and so it can act as a DONOR of this carboxy (COO-) group.
Biotin/B7 summary slide:
- Biotin is cofactor for the transfer of carbon dioxide in several carboxylation reactions
- Active form is covalently bound to lysine residues of enzymes
- Dietary deficiency is UNKNOWN - very small amount is needed - widespread in food
- **UNCOOKED EGG WHITES contain AVIDIN, which BINDS BIOTIN TIGHTLY and can INDUCE BIOTIN DEFICIENCY (biotech companies use avid to bind tightly to biotin when making things/they tag them with biotin and then use avidin)
- ***GENETIC DEFECT in BIOTINIDASE, the enzyme that cleaves biotin from proteins, leads to BIOTIN DEFICIENCY (because when we ingest biotin it is usually covalently linked to protein, and we need this enzyme to break it off the protein so we can absorb it)….this is one of diseases that is screened for in genetic testing (next week’s topic)
Vitamin C
Three forms of vitamin C (ascorbate, ascorbic acid, and dehydroascorbic acid)
-Discovered by it’s ability to cure SCURVY
***Scurvy: gums weak and bleeding, general defect in connective tissue
-Problem: Collagen, the protein component of
connective tissue, is unstable in scurvy
-Vitamin C is required by hydroxylases that convert procollagen to collagen
-Other roles of vitamin C
*antioxidant
*Accepts and donates electrons
-reduces ferric iron back to active ferrous state (this enhances iron absorption)
*Hydroxylation of carnitine
*Needed for synthesis of thyroid hormone and cholecystokinin (CCK)
*neurotransmitter norepinepherine
Food Sources of Vitamin C
-Citrus fruits, cabbage-type vegetables, dark green vegetables, strawberries, tomatoes, potatoes
TOXICITY
- Amounts under 2g/day are okay - Nausea, cramps, diarrhea - Other concerns: * May increase kidney stones in some people * May adversely affect those with iron overload
stopped 18.55 vitamin A
finish later go to 19min
