WATER SOLUBLE VITAMINS

 Vitamin B complex

Vitamin B complex consists of a number of water- soluble vitamins which act as co-factors for various biochemical reactions in our body. In this section we will learn about some of these B complex vitamins including Thiamin€ (Vitamin B1), Riboflavin (Vitamin B2), Niacin (Vitamin B3), Pyridoxine (Vitamin B6), Cobalamin (Vitamin B12) and Folic acid. Biotin and Pantothenic acid also belong to this complex. Some of them, B1, B2, B3, B6, pantothenic acid, biotin, are known as energy releasing vitamins because of their involvement in energy yielding metabolic pathways, while folic acid and B12 are referred to as hematopoietic vitamins as they are required for synthesis of red blood cells in the body.

Thiamin(e) 

Thiamin(e) or vitamin B1 is also called as anuerine. It is a sulphur containing vitamin and thus named thio vitamin or thiamine. In 1926, Dutch physician Christian Eijkman recognised thiamine as anti- beriberi factor. This is a colorless compound with a chemical formula C12H17N4OS. Its structure contains a pyrimidine ring and a thiazole ring that is joined by methylene group (Fig. 7.1). Thiamine is synthesized in bacteria, fungi and plants. It is required for aldehyde transfers, and thus needed for the metabolism of carbohydrate, fats and proteins.

Biochemical function

Thiamine pyrophosphate or TPP (also called Thiamin diphosphate or TDP) is an active coenzyme form of vitamin B1. Thiamine-dependent reactions are aldehyde transfers. The aldehyde is bound covalently to one of the carbons in the thiazole ring. The reactions that require TPP include oxidative decarboxylation, decarboxylation, transketolase reactions etc. 

TPP serves as an important cofactor for enzymes such as transketolase, pyruvate dehydrogenase (PDH), and α– ketoglutarate dehydrogenase. For example, TPP dependent pyruvate dehydrogenase catalyzes the oxidative decarboxylation of pyruvate into acetyl coenzyme A