10.1.1. Thiamine

10.1.1. Thiamine

Thiamine consists of a substituted nitrogen-containing ring pyrimidine (2,5-dimethyl 6 amino pyrimidine) joined by a methylene bridge to substituted sulphur containing ring thiazole (4methyl 5 hydroxyethyl thiazole). Thiamine pyrophosphate (TPP) is the coenzyme formed from thiamine.

Thiamine

Functions

1. TPP participates in decarboxylation, which removes a carboxyl group (-COOH) and releases it as CO2. During glucose metabolism, for example, decarboxylation removes one carbon from the three carbon pyruvate to form the two carbon compound acetyl CoA catalysed by the enzyme pyruvate dehydrogenase.

2. TPP is involved in the oxidative decarboxylation of -ketoglutarate to succinyl CoA ketoglutarate dehydrogenase in citric acid cycle, in the pentose phosphate pathway, in the reaction catalysed by transketolase, in the oxidative decarboxylation of the -ketocarboxylic acid derivatives of the branched-chain amino acids (leucine, isoleucine, and valine).

3. TPP plays a role in nerve function. All of these reactions are inhibited in thiamine deficiency.

Deficiency: Polyneurities or beriberi is a deficiency disease of thiamine. It causes loss of appetite and other symptoms such as irritability, fatigue and dizziness. Different forms of beri beri are dry beriberi, wet beriberi and infantile beriberi.

i) Dry beriberi: Dry beriberi is characterized primarily by emaciation and multiple neurotic symptoms which proceed from foot, then to calf muscles and then to the thigh. The muscle becomes wasted and weak and difficult to walk.

ii) Wet beriberi: Wet beriberi is characterized by a severe edema which masks the emaciation, enlargement of heart, tachycordia, anorexia, dyspepsea and palpitations of the heart even on the slightest exertion. The nervous system is badly affected and this may produce partial paralysis and muscular weakness.

iii) Infantile beriberi: This occurs in breast fed infants between 2nd and 5th months.

RDA Infants :

 Inflants :0.3-0.5mg

Children :0.7-1.2mg

Adult (male) :1.2-1.5mg

Adult (female) :1.0-1.1mg

Pregnant and lactating women :1.3-1.5mg

Sources

Good sources: Unrefined cereals, pulses, nuts, oilseeds

Fair sources: Meat, fish, eggs, milk, fruits and vegetable. Thiamine deficiency is found frequently in chronic alcoholics consuming little other food.

Certain raw fish contain a heat-labile enzyme (thiaminase) that destroys thiamine, but this enzyme is destroyed by cooking.

Last modified: Saturday, 12 November 2011, 7:59 AM