B-Complex Vitamins Flashcards
Most B vitamins are ________ in ________ ___________ __________
coenzymes; cellular enzyme metabolism
General B-complex deficiency symptoms
-loss of appetite (anorexia)
-poor growth
-emaciation
-nerve related disorders
-dermatitis
-anemia
Vitamin B1
Thiamine
What is the principle role of Thiamine?
part of the coenzyme cocarboxylase (TPP)
-TPP is the coenzyme for at least 24 enzyme systems
Thiamine is closely related to _______ ________
Lipoic acid
Lipoic acid
an essential component of a “multienzyme” system which is involved in the oxidative decarboxylation of keto acids
What occurs with pyruvic acid before its entrance into the TCA cycle?
it must be decarboxylated and then combined with coenzyme A to form acetyl CoA
What happens in the absence of Thiamine?
reactions do not proceed at a normal rate so pyruvic acid and lactic acid accumulate in the blood and tissues
-this increase in acids is responsible for deficiency symptoms in metabolically active tissue like muscle and nerve
Beriberi
-thiamine deficiency disease in humans
-extensive damage to nervous and cardiovascular systems
-severe muscle wasting (dry beriberi
-edema (wet beriberi)
Polyneuritis
-Thiamine deficiency disease
-in birds
-accumulation of intermediates of CHO metabolism
-a peripheral nerve degeneration as evidenced by the breakdown of the myelin sheaths of the nerve fibers
Thiamine deficiency symptoms
-beriberi
-polyneuritis
-soft muscles
-anorexia or loss of appetite
-weight loss
-bradycardia (reduced heart rate) and enlargement of heart
Thiamine requirements are influenced by
carbohydrate intake and caloric intake
Thiamine is readily destroyed by ________ in the presence of moisture
heat (cooking)
Thiamin deficiency in North America is largely associated with…
chronic alcoholism
Where is Thiamine absorbed?
small intestine
What happens to thiamine after it is absorbed?
carried to the liver and phosphorylated to form TPP
Where is thiamine stored?
it is not stored and must have a daily intake (except for in the pig)
What is thiamine’s role in ruminants and horses?
-in a functional rumen bacterial synthesis of B1 is adequate
-in the cecum and LI of the horse bacterial synthesis occurs
-synthesis is not adequate for nutritional needs alone, dietary intake is still necessary
Pyrithiamine
-antivitamin of thiamine
-competes with thiamine for incorporation into the enzymes thus rendering the enzyme inactive
Chastek paralysis
-in foxes
-due to an antagonistic action of thiaminase
-similar to “bracken fern poisoning” in horses
Thiamine sources
-mainly from plants
-yeasts (richest)
-molds
-leaves of grasses
-germ of cereal grains
-seed coats of grains
-pork has 100x the amount in beef
Vitamin B2
riboflavin
What 2 coenzymes does riboflavin act as
-FMN - flavin mononucleotide (1 phosphate group)
-FAD - flavin adenine dinucleotide (2 phosphate groups)
What are the flavin coenzymes concerned with?
donating and accepting H atoms
-FAD function with the enzyme succinic dehydrogenase
What other enzymes is FAD a constituent of?
-D-amino acid oxidase
-glycine oxidase
-xanthine oxidase (purine to uric acid)
What is different about the symptoms of riboflavin deficiency to thiamine deficiency?
it is not possible to relate the symptoms to the biochemical roles of riboflavin
Riboflavin deficiency symptoms
-decrease growth
-alopecia or hair loss in rats
-opaque cornea or cataracts in humans
-curled toe paralysis in chicks
-low egg production and hatchability
-skin and eye symptoms in man
What are the skin and eye symptoms of riboflavin deficiency in humans?
-cheilosis = roughened skin and furrows around the mouth
-dermatitis = due to overactivity of sebaceous or oil glands and results in waxy dermatitis of eyes, ear lobes, and mouth
-corneal vascularization = due to increase blood vessels in the eye
Where is riboflavin phosphorylated?
in the intestinal wall
After phosphorylation what happens to riboflavin?
it is carried by the blood to the cells of the tissues where it occurs as the phosphate or as a flavoprotein
Where is riboflavin stored?
storage is small and excessive intakes are rapidly excreted in urine
Sources of riboflavin
-yeast (richest)
-milk
-leafy portions of plants like alfalfa
-eggs, liver, heart, kidney, and meat muscle (richest animal products)
-whey and distiller’s solubles
What/Who synthesizes riboflavin?
-higher plants
-yeasts
-fungi
-some bacteria
-ruminants synthesize inadequate amounts
-horses synthesize inadequate amounts in cecum
Vitamin B6
pyridoxine
What results in substantial loss of the 3 pyridoxine compounds?
sterilization of milk
Three forms of vitamin B6
-pyridoxine
-pyridoxal
-pyridoxamine
What are the active forms of vitamin B6
pyridoxal phosphate and pyridoxamine phosphate
(pyridoxal is the most active)
Where are the forms of B6 phosphorylated?
in the liver after absorption
(once phosphorylated, interconversion is possible)
What does pyridoxal phosphate mainly function as?
a coenzyme in several enzyme systems concerned with protein/amino acid metabolism
Pyridoxal phosphate is necessary in the process of ___________
transamination
Transimination
a process that involves the transfer of the amino group to keto acids
-most abundant catalyze transamination of glutamic acid to oxaloacetic and pyruvic acids
Pyridoxal phosphate is involved in ______________ reactions
decarboxylation
-serves as a coenzyme (codecarboxylase) which decarboxylates several amino acids
-more abundant in microorganisms than animal tissues
B6 is involved in the synthesis of ________ from ___________
niacin from tryptophan
In the absence of B6 what forms instead of niacin?
xanthurenic acid is formed and excreted in the urine
-level of this metabolite in urine can be used as an indicator of B6 nutrition
What are the two antivitamins of B6?
-desoxypyridoxine
-isoniazid (drug used in the treatment of tuberculosis)
-compete with B6 for the active site on the apoenzyme
Vitamin B6 deficiency symptoms
-growth failure
-acrodynia (dermatitis) in rats
-urinary calculi (especially in cattle)
-anemia in dogs, pigs, and rats
-convulsions or epileptic seizures
-slow growth and suppressed appetite
Acrodynia
-dermatitis of tails, ears, mouth, and paws accompanied by an edema
-the edema distinguishes acrodynia from dermatitis of essential fatty acid deficiency
Urinary calculi
-due to defect in glycine metabolism
-high insoluble Ca oxalate precipitates out as “stones” in kidney and urinary tract
What causes the anemia caused by vitamin B6?
inability to condense glycine with succinyl CoA to form a-amino-B-ketoadipic acid which is the initial step in heme synthesis so microcytic hypochromic anemia results
Sources of B6
-yeast
-liver
-muscle meat
-milk
-cereal grains
-food supply is usually so rich in B6 that practical rations are very unlikely to cause deficiency
