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Chapter-34 Water Soluble Vitamins (Thiamine, Riboflavin, Niacin, Pyridoxine, Pantothenic acid, Biotin, Folic acid, Vitamin B12 and Ascorbic acid)

BOOK TITLE: Textbook of Biochemistry for Medical Students

Author
1. Vasudevan DM
2. S Sreekumari
3. Vaidyanathan Kannan
ISBN
9789350250167
DOI
10.5005/jp/books/11359_34
Edition
6/e
Publishing Year
2011
Pages
20
Author Affiliations
1. Faculty of Medicine, Amrita Vishwa Vidyapeetham, (Amrita University), Kochi, Kerala, College of Medicine, Amrita Institute of Medical Sciences, Cochin, Kerala; (Formerly Principal, College of Medicine, Amrita, Kerala); (Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim), Amrita Institute of Medical Sciences, Kochi, Kerala, India, Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, E-mail: dmvasudevan@aims.amrita.edu, College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, Amrita School of Medicine, Amrita Institute of Medical Sciences; Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, Amrita Vishwa Vidyapeetham (Amrita University), kochi, Kerala; College of Medicine, Amrita Institute of Medical Sciences, Cochin, Kerala, College of Medicine, Amrita Institute of Medical Sciences, Cochin, Kerala, India
2. Jubilee Mission Medical College, Thrissur, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India, Jubilee Mission Medical College, Trissur, Kerala, Jubilee Mission Medical College, Thrissur (Kerala)
3. Amrita Institute of Medical Sciences, Kochi, Kerala, Amrita Institute of Medical Sciences, Kochi, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Center, Thiruvalla, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India
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Abstract

The co-enzyme form of Thiamine is thiamine pyro phosphate (TPP). TPP is essential for PDH, transketolase, alpha ketoglutarate dehydrogenase. Deficiency of thiamine leads to beriberi. Co-enzyme forms of riboflavin are FMN and FAD. Examples of FAD dependent enzymes are succinate dehydrogenase and acyl CoA dehydrogenase. Examples of NAD+ dependent enzymes are lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase and pyruvate dehydrogenase. Niacin is synthesized from tryptophan. In Hartnup disease, tryptophan absorption from intestine is limited. This leads to deficiency of tryptophan and consequently of nicotinamide. Active form of pyridoxine is pyridoxal phosphate (PLP). PLP is essential for transamination and decarboxylation reactions of amino acids. ALA synthase in heme biosynthesis is also a PLP dependent enzyme. Hence anemia is common in B6 deficiency. Isonicotinic acid hydrazide (INH) (isoniazid) used as an antituberculosis drug can produce pyridoxine deficiency. Co-enzyme A contains pantothenic acid. Important CoA derivatives are acetyl CoA, succinyl CoA, HMG CoA and acyl CoA. Biotin acts as co-enzyme for carboxylation reactions, e.g. acetyl CoA carboxylase, propionyl CoA carboxylase, pyruvate carboxylase. Avidin, a protein present in egg white has great affinity to biotin. Hence intake of raw (unboiled) egg may cause biotin deficiency. THFA (tetrahydro folic acid) is the carrier of one-carbon groups. Macrocytic anemia is the most characteristic feature of folate deficiency. FIGLU excretion test is used for assessment of folate status in man. Folate antagonists are Sulphonamides, Trimethoprim, Pyrimethamine, Aminopterin and Amethopterin. Absorption of Vitamin B 12 requires the intrinsic factor (IF) of Castle. Transcobalamin-II, a glycoprotein, is the specific carrier of Vitamin B 12. Vitamin B 12 containing enzymes in the human body are methyl malonyl CoA isomerase and homocysteine methyl transferase. B12 deficiency leads to pernicious anemia. Man, higher primates, guinea pigs and bats are the only species which cannot synthesise ascorbic acid (vitamin C). Scurvy is characterized by abnormal collagen, ecchymosis, hemorrhage and anemia.

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