Vitamin b1

Vitamin B1 introduction, chemistry, Biochemical role, Dietary sources, Recommended dietary Allowance, Deficiency symptoms of Vitamin B1, Hypervitaminosis, Toxicity of Vitamin B1

1. Chemistry and Biochemical role, RDA and Deficiency diseases of Vitamin B1 Jasmine Juliet .R Biotechnology Department Agricultural college and Research & Institute Madurai .

2. Thiamine (Vitamin B1 ) - Introduction Thiamine (anti- beri beri or antinuritic vitamin) is water soluble . It has a specific coenzyme , Thiamine pyrophosphate ( TPP or cocarboxylase ) which is mostly associated with carbohydrate metabolism.

3. Thiamine (Vitamin B1) - Chemistry Thiamine is soluble in water and easily destroyed by heat or oxidation especially in the presence of baking soda. The term Thiamine indicates that it is a sulphur - and nitrogen- containing substance. Thiamine contains a pyrimidine ring and a thiazole ring held by a methylene bridge.

4. Thiamine (Vitamin B1) - Chemistry Thiamine is the only natural compound with thiazole ring. The alcohol (OH) group of thiamine is esterified with phosphate (2 moles) to form the coenzyme , Thiamine pyrophosphate (TPP or cocarboxylase ). The pyrophsphate moiety is donated by ATP and the reaction is catalysed by the enzyme thiamine pyrophosphate transferase .

5. Thiamine (Vitamin B1) - Biochemical functions (I) The coenzyme, Thiamine pyrophosphate or cocarboxylase is intimately connected with the energy releasing reactions in the carbohydrate metabolism. (II) The enzyme Pyruvate dehydrogenase catalyses ( Oxidative decarboxylation ) the irreversible conversion of pyruvate to acetyl CoA . This reaction is dependent on TPP, besides the other coenzymes.

6. Thiamine (Vitamin B1) – Biochemical functions (III) α - Ketoglutarate dehydrogenase is an enzyme of the citric acid cycle. This enzyme is comparable with pyruvate dehydrogenase and requires TPP. (IV) Transketolase of the hexose monophosphate shunt is dependent on TPP.

7. Thiamine (Vitamin B1) – Biochemical Functions (V) The branched chain α - Keto acid dehydrogenase ( decarboxylase ) catalyses the oxidative decarboxylation of branched chain aminoacids ( Valine , Leucine , and isoleucine ) to the respective keto acids. This enzyme also requires TPP.

8. Thiamine (Vitamin B1) – Biochemical Functions (VI) TPP plays an important role in the transmission of nerve impulse. It is believed that TPP is required for acetylcholine sythesis and the ion translocation of neural tissue.

9. Thiamine (Vitamin B1) – Biochemical Functions (VII) Thiamine plays a role in the conversion of the aminoacid tyrptophan to Niacin. (VIII) Thiamine has several indirect functions in the body because of its role in energy metabolism like: Maintenance of appetite. Maintenance of muscle tone Maintenance of healthy mental attitude.

10. Thiamine (Vitamin B1) - Recommended dieary allowance (RDA) The daily requirement of thiamine depends on the intake of carbohydrate . A dietary supply of 1-1.5mg/day is recommended for adults (about 0.5mg/1000cals of energy).

11. Thiamine (Vitamin B1) – Dietary Sources Cereals , pulses, oil seeds, nuts and yeast are good sources . Polishing of rice removes about 80% of Thiamine. Vitamin B1 is also present in animal foods like pork, liver, heart, kidney, milk, etc.

12. Thiamine (Vitamin B1) – Deficiency Symptoms The deficiency of vitamin B1 results in a condition called Beri-Beri . Beri-Beri is mostly seen in populations consuming exclusively polished rice as staple food.

13. Thiamine (Vitamin B1) – Deficiency Symptoms The early symptoms of Thiamine deficiency are: L oss of appetite (anorexia), W eakness , C onstipation , N ausea, M ental depression, Peripheral neuropathy, Irritability , etc. Numbness in the legs complaints of ‘pins and needles sensations ’ are reported.