BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 8. VITAMINS

8.1. Classification and General Properties of Vitamins

8.1.1. Classification of Vitamins

Traditionally, Vitamins are divided into two groups based on their physicochemical properties: Water-soluble and fat-soluble. Water-Soluble Vitamins include all B-complex vitamins—thiamine, riboflavin, pantothenic acid, niacin (nicotinamide), pyridoxine, cobalamin, folic acid—as well as Vitamin C (ascorbic acid) and vitamin H (biotin). Fat-soluble vitamins include vitamins A, D, E, and K. Some BIOLOGICALLY ACTIVE SUBSTANCES are classified as Vitamin-like compounds.

The discovery of vitamins took place in the late 19th and early 20th centuries As a result of investigating various diseases such as beri-beri, pellagra, Rickets, and others. It was not until the 1960s and 1970s that the rapid development of biochemistry uncovered the metabolic role of most water-soluble vitamins as Coenzymes and prosthetic groups. The fundamental mechanisms of biochemical reactions and The Structure of coenzymes were elucidated, and molecular Mechanisms of Enzymatic Catalysis involving active forms of vitamins were proposed. Later, significant progress was also made in studying the MOLECULAR MECHANISMS OF action of fat-soluble vitamins, which led to a new Classification based on The Nature of their specific biological Functions. According to this classification, vitamins are divided into three groups:

1) coenzyme vitamins (thiamine, riboflavin, niacin, pyridoxine, folic acid, pantothenic acid, biotin, cobalamin, vitamin K),

2) antioxidant vitamins (vitamin C, vitamin E, carotenoids),

3) prohormone vitamins (vitamins D, vitamins A).

This division is somewhat arbitrary, as the polyfunctional nature of certain vitamins allows them to be assigned to two classes simultaneously. For example, vitamin C (ascorbic acid) is not only an antioxidant but also acts as a cofactor in hydroxylation reactions.

Inadequate or poor Nutrition and/or impaired absorption and utilization of vitamins can lead to Various Forms of vitamin deficiency.

Avitaminosis refers to disorders that occur in the case of a complete absence of a vitamin in the diet or impaired absorption.

Hypovitaminosis is caused by insufficient intake or partial impairment of vitamin absorption.

Hypervitaminosis is associated with excessive intake of a vitamin into The Human Body.

Insufficient Dietary intake of vitamins is a widespread problem in all developed countries. It has arisen, firstly, due to a decrease in Energy Expenditure and, consequently, a reduction in total food intake, and secondly, due to advancements in food technology that have led to more refined food products.

No vitamin can perform its metabolic functions in the exact form in which it is ingested with food. Before fulfilling its functions, a vitamin must undergo specific stages involving specialized transport, enzymatic, and receptor Proteins. To date, A large number of proteins are known to participate in gastrointestinal absorption, Blood transport, transmembrane crossing, and The conversion of vitamins into their active coenzyme or hormonal forms. Most water-soluble vitamins are precursors of coenzymes that function in METABOLISM in cooperation with corresponding apoenzymes. The active metabolites of fat-soluble vitamins (A, D) function as Hormones.

Currently, a wide range of Inherited Disorders of vitamin metabolism are also known—the so-called vitamin-dependent and vitamin-resistant states, the Clinical presentation of which resembles typical avitaminosis. The underlying cause is Genetic Defects in proteins responsible for the absorption, transport, and conversion of vitamins into their active forms.