Biochemistry

Thiamine (vitamin B b antineuritic factor). This was the first object of research, on the basis of which the whole group was called "vitamins." Thiamine was isolated from rice bran in 1926, and it was synthesized in 1937. Structure and physicochemical properties. The thiamine molecule consists of a pyrimidine base and a thiazole ring. Both cycles are interconnected by a methylene group. This vitamin is a derivative of thiazole (4-methyl-5- hydroxyethylthiazole) and pyrimidine (5-methyl-5-hydroxymethyl-6- aminopyrimidine) . nh 2 I \ * N C-CH.-N ---- C-CH, I II II II H,C — C CH HC C-CH,-CH 2 -OH N S Pyrimidine cycle Thiazole cycle Thiamine In the above formula, vitamin В exists in an acidic medium; a different structure is characteristic for neutral and alkaline. Thiamine is a colorless crystal with bitter taste, readily soluble in water, ether, chloroform. Aqueous solutions of thiamine are stable in an acidic medium and can withstand heating to a high temperature (130-140 °C). In neutral and especially in alkaline medium, it is rapidly destroyed at 80-100 °C. This explains the decrease of thiamine content during cooking food (for example, when baking bread with the addition of ammonium carbonate or sodium bicarbonate). When thiamine is oxidized, thiochromide is formed, which gives blue fluorescence in ultraviolet light, so that it can be quantified. Biological role. Thiamine is involved in the regulation of carbohydrate, protein, fat and water-salt metabolism. The biological effect of thiamine is associated with its diphosphate ester (thiamine diphosphate (TDF) and thiamine pyrophosphate (TPP). Thiamine pyrophosphate is formed by the mediation of thiamine pyrophosphokinase, which transfers the remainder of the pyrophosphate from ATP to thiamine. 246 J