د.سرى كيمياء حياتية 10\10\2017
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Vitamin B6
HYPER13 INCLUDEPICTURE "I:\\Biochemisy_2003 (G)\\dll\\pyridoxal.jpg" \* MERGEFORMATINET INCLUDEPICTURE "I:\\Biochemisy_2003 (G)\\dll\\pyridoxamine.jpg" \* MERGEFORMATINET PyridoxinePyridoxalPyridoxamine
Pyridoxal, pyridoxamine and pyridoxine are collectively known as vitamin B6. All three compounds are efficiently converted to the biologically active form of vitamin B6, pyridoxal phosphate. This conversion is catalyzed by the ATP requiring enzyme, pyridoxal kinase.
INCLUDEPICTURE "I:\\Biochemisy_2003 (G)\\dll\\pyridoxalphosphate.jpg" \* MERGEFORMATINET Pyridoxal Phosphate
Distribution of vitamin B6:
Pyridoxine occurs primarily in plants whereas pyridoxal and pyridoxamine are found in foods obtained from animals
Functions of Pyridoxal phosphate:
Pyridoxal phosphate functions as:1. A cofactor for enzymes that catalyze reactions involving amino acids.
A. transamination reactions: e,g ALT and AST enzymes. :oxaloacetate+glutamate↔aspartate+ketogluterate
B. deamination : serine→pyrovate+NH3
C. Decaboxylation: Histidine→histamine+CO2
D. condensation: glycine+succinyl CoA →aminlevulinic acid
In glycogenolysis as a cofactor for glycogen phosphorylase.
Deficiencies of vitamin B6 are rare and usually are related to an overall deficiency of all the B-complex vitamins.Vitamin B6 deficiency lead to glossitis and peripheral neuropathy.
Biotin :
INCLUDEPICTURE "I:\\Biochemisy_2003 (G)\\dll\\biotin.jpg" \* MERGEFORMAT Biotin
SOURCES:
( Widespread in foods
( Meats, egg yolks, soybeans, fish, whole grains
( Also produced by Intestinal bacteria
Function of biotin:
Biotin is the cofactor required of enzymes that are involved in carboxylation reactions, in which it serves as carrier of activated carbon dioxidee.g. acetyl-CoA carboxylase and pyruvate carboxylase.
*Active form of Biotin acts as coenzyme for CARBOXYLATION Reactions (addition of carbon in the form of carbondioxide).
*Carboxylation of Acetyl CoA ( Biosynthesis of Fatty Acids)
Acetyl CoA + CO2 Malonyl CoA
Biotin is found in numerous foods and also is synthesized by intestinal bacteria and as such deficiencies of the vitamin are rare.
symptoms of biotin deficiency :
Dermatitis, glossitis, loss of appetite, and nausea.
Causes of Deficiency:
Avidin: A protein present in the raw egg white has great affinity to biotin, and tightly bounds biotin preventing its absorption from the intestine.
Prolonged use of Antibiotics kills the intestinal bacteria resulting in decreased biotin synthesis.
Ascorbic Acid (vitamin C):
INCLUDEPICTURE "I:\\Biochemisy_2003 (G)\\dll\\ascorbicacid.jpg" \* MERGEFORMATINET Ascorbic Acid
Ascorbic acid is more commonly known as vitamin C.
Vitamin C is Found
Mostly in citrus fruit and juices (lemons, oranges, peaches, strawberries, bananas, and grapefruits)
Also in cabbage, broccoli, cauliflower, leaf lettuce, tomatoes, potatoes, and beans.
There are also vitamin C pills and other things for supplements.
Vitamin C is probably the least stable of the water soluble vitamins, it is particularly liable to heating.it is stable to freezing.
Ascorbic acid can be synthesized in a variety of plants and in all animals except primates. Human unable to synthesize ascorbic acid so it should be supplied in diet.
The active form of vitamin C is ascorbate acid itself.
Metabolism of vitamin C:
Vitamin C is readily absorbed in the intestine, and a deficiency of it is therefore attributable to inadequate dietary intake. The major excretory products of ascorbic acid are ascorbic acid itself and dehydroascorbate.
Function of vitamin C:
anti-oxidant :The main function of ascorbate is as a reducing agent (anti-oxidant) in a number of different reactions. Vitamin C has the potential to reduce cytochromes a and c of the respiratory chain as well as molecular oxygen.cofactor:
a. The most important reaction requiring ascorbate as a cofactor is the hydroxylation of proline residues in collagen. Vitamin C is, therefore, required for the maintenance of normal connective tissue as well as for wound healing since synthesis of connective tissue is the first event in wound tissue remodeling. Vitamin C also is necessary for bone remodeling due to the presence of collagen in the organic matrix of bones.
b. Several other metabolic reactions require vitamin C as a cofactor. These include the catabolism of tyrosine and the synthesis of epinephrine from tyrosine and the synthesis of the bile acids.
3. It is also believed that vitamin C is involved in the process of steroidogenesis since the adrenal cortex contains high levels of vitamin C which are depleted upon adrenocorticotropic hormone (ACTH) stimulation of the gland.
4.aids in iron absorption , active folicacid ,
5.aids in drug metabolism and detcoxi fication
Other function of vitamin C:
Aids in iron absorption
Activates folic acid
Aids in drug metabolism and detoxification
Deficiency in vitamin C:
Deficiency in vitamin C leads to the disease scurvy.
Scurvy is characterized by:
easily bruised skin,
muscle fatigue,
soft swollen gums,
decreased wound healing and hemorrhaging,
osteoporosis,
and anemia.
Scurvy was common among sailor in the 18thand 19th centuries who spent along time at sea with out fresh fruits and vegetables
Summary:
the biologically active form of vitamin B6, pyridoxal phosphate.
Pyridoxal phosphate functions as: A cofactor in enzymes involved in transamination ,deamination , decarboxylation and condensation reactions and in glycogenolysis
Biotin is the cofactor required of enzymes that are involved in carboxylation reactions
The active form of vitamin C is ascorbate acid itself.
Function of vitamin C: as anti-oxidant and cofactor
Deficiency in vitamin C leads to the disease scurvy