Answer- Vitamin B6 serves as a coenzyme of approximately 100 enzymes that catalyze essential chemical reactions in the human body. It plays an important role in protein, carbohydrate and lipid metabolism. Pyridoxal phosphate is a coenzyme for many enzymes involved in amino acid metabolism, especially transamination, deamination and decarboxylation reactions. It is also the cofactor of glycogen phosphorylase.
2- Which out of the two oxidases, L-Amino acid Oxidase or D- amino acid Oxidase, require FMN as a prosthetic group?
Answer- L-amino acid oxidases require FMN while FAD is required by D- Amino acid oxidases.
3- What is the cause for neurological manifestations in B6P deficiency?
Answer- It is required for the synthesis of neurotransmitters like Serotonin, GABA (Gamma amino butyric acid) and also Dopamine, norepinephrine and epinephrine . These are produced by decarboxylation reactions .B6-P is also required for the synthesis of sphingomyelins and other sphingolipids that are required for the formation of myelin sheath. Therefore deficiency of B6-P results in impairment of such reactions and hence neurological deficit.
4- What are the different forms in which the disease Beriberi can be manifested ?
Answer- Beriberi is the outcome of vitamin B1(thiamine) deficiency. It is manifested as dry, wet, infantile, cerebral (Wernicke’s Korsakoff syndrome) or shoshin beriberi.
5- Which vitamin deficiency, B6 or B12 is associated with Homocystinuria?
Answer- Homocystinuria is associated with deficiencies of both B6 and B12. It is also associated with folic acid deficiency. The remethylation of homocysteine back to methionine is B12 and folic acid dependent, (Homocystine is a dimer), while further metabolism of homocysteine is B6 dependent. Thus deficiency of any of these vitamins can cause accumulation of homocysteine in blood and also excessive excretion in urine (dimeric form).
6- Which vitamin is required for the synthesis of bile salts from cholesterol?
Answer- Vitamin C (ascorbic acid) is required for the activity of 7-α hydroxylase, the key regulatory enzyme of bile acid synthesis from cholesterol. Bile salts are produced from bile acids.
7- Name the vitamin required as a coenzyme for the conversion of Pyruvate to Oxaloacetate?
Answer- Biotin is required as a coenzyme, since it is a carboxylation reaction catalyzed by pyruvate carboxylase enzyme. This is the first step of gluconeogenesis.
8- What is the cause of reduced RBC Transketolase activity in Thiamine deficiency?
Answer- Transketolase enzyme is the enzyme of HMP pathway, a pathway of glucose utilization. Thiamine as TPP (active form- Thiamine pyrophosphate form) is required as a coenzyme for the functioning of this enzyme. In thiamine deficiency, the activity of this enzyme goes down and that is estimated in red blood cells to diagnose the underlying deficiency.
9- Why are alcoholics more prone to Thiamine deficiency?
Answer- Reduced dietary intake and impaired absorption are the important causes of thiamine deficiency in chronic alcoholics.
10- Which vitamin deficiency can be detected by Tryptophan load test?
Answer- Tryptophan load test is undertaken to diagnose underlying B6-P deficiency. Tryptophan is given as a loading dose and the amount of xanthurenic acid excreted in urine is estimated. In B6 deficiency, the amount of xanthurenic acid excreted in urine is increased (Xanthurenic acid is normally produced in a very small amount, but it is produced in excess in B6 deficiency.)
11- Which water soluble vitamin participates in the transfer of one carbon fragments?
Answer- Folic acid is the carrier of one carbon fragments. Tetrahydrofolate can carry one-carbon fragments attached to N-5 (formyl, formimino, or methyl groups), N-10 (formyl) or bridging N-5–N-10 (methylene or methenyl groups).
12-Which vitamin participates in decarboxylation reactions of amino acids?
Answer- Decarboxylation reactions of amino acids are catalyzed by decarboxylases that require B6 as a coenzyme. The neurotransmitters serotonin, GABA, Dopamine, norepinephrine and epinephrine are produced by decarboxylation of amino acids.
13- Which vitamin deficiency leads to impaired coagulation of blood?
Answer- Vitamin K is required for coagulation of blood. Vitamin K deficiency is the cause of bleeding tendencies and impaired coagulation of blood.
14- What is the basis of supplementation with Folic acid, B12 and B6 to prevent IHD?
Answer- Folic acid, B12 and B6 participate in the metabolism of homocysteine. Excess of homocysteine has atherogenic effect and increases the tendency for ischemic heart disease in the high risk people or people having family history of IHD. Deficiency of any of these vitamins can cause accumulation of homocysteine in blood, thus as a precaution these vitamins are supplemented to prevent the trigger of atherosclerosis by hyperhomocysteinemia.
15- What are the toxic effects of high dose niacin therapy?
Answer- Prostaglandin-mediated flushing due to binding of the vitamin to a G protein–coupled receptor has been observed at daily doses as low as 50 mg of niacin when taken as a supplement or as therapy for dyslipidemia. It may be more intense after alcohol ingestion, aerobic activity, sun exposure, and consumption of spicy foods. There is no evidence of toxicity from niacin derived from food sources. Flushing always starts in the face and may be accompanied by skin dryness, itching, paresthesias, and headache. Premedication with aspirin may alleviate these symptoms. Nausea, vomiting, and abdominal pain also occur at similar doses of niacin. Hepatic toxicity is the most serious toxic reaction due to niacin and may present as jaundice.
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