Vitamins in biochemistry

General Characteristics of Vitamins

Group B vitamins are water-soluble, biologically active substances with a low molecular weight. Their primary functional role is acting as coenzymes or their precursors. Vitamins themselves do not possess high biocatalytic activity; it is acquired by the products of their biotransformation in the body.

Participating in metabolism and regulating assimilation processes, these compounds act as biological catalysts. Based on their derivatives, medications for metabolic therapy have been developed, such as flavinate ($B_2$), pyridoxal phosphate ($B_6$), cobalamide ($B_{12}$), and cocarboxylase ($B_1$). Their advantage lies in being natural metabolites with low toxicity.

Role in Enzyme Systems

In the body, vitamins function as micronutrients and essential dietary factors supplied in trace amounts. They ensure the progression of key biochemical processes without being consumed as energy sources or incorporated into tissue structures.

Many metabolic disorders in vitamin deficiency are directly linked to impaired enzyme system activity. This is because vitamins form part of prosthetic groups or coenzymes, without which the catalytic activity of enzymes becomes impossible.

Involvement of Vitamins in Serotonin Metabolism

Certain vitamins are directly involved in the synthesis and conversion of vital neurotransmitters. A striking example is the formation of serotonin (5-hydroxytryptamine):

1. At the first stage, tryptophan is hydroxylated to 5-hydroxytryptophan with the participation of the enzyme tryptophan hydroxylase and the coenzyme tetrahydrobiopterin ($H_4$BH4).
2. At the second stage, 5-hydroxytryptophan is decarboxylated to form serotonin. This process is catalyzed by aromatic amino acid decarboxylase, with pyridoxal phosphate (PLP, or vitamin B6) acting as the coenzyme.

Subsequently, the inactivation of serotonin via oxidative deamination to 5-hydroxyindoleacetic acid is carried out by the enzyme MAO, which utilizes the coenzyme FAD (flavin adenine dinucleotide).

Pharmacological Aspects of Biogenic Amine Metabolism

The mechanism of action of certain drugs is based on the modulation of enzyme systems associated with vitamin coenzymes. For example, St. John's wort preparations (Deprim, Negrustin) contain hypericin and flavonoids that inhibit the enzyme MAO (monoamine oxidase).

When MAO is inhibited, the breakdown of biogenic amines slows down, leading to an increase in their concentration in the synaptic cleft and the nervous system, improving mood and exerting an antidepressant effect.

Class and exam questions

What else to study on this topic

• Structure and Chemical Properties of Vitamins B1, B2, B6, PP, Biotin, and Pantothenic Acid
• Clinical Signs of Avitaminosis and Hypovitaminosis of Group B
• Role of Monoamine Oxidase (MAO) and Its Isoenzyme Types in Catecholamine Inactivation
• Mechanisms of Synaptic Transmission and the Role of Serotonin in the Central Nervous System and Gastrointestinal Tract
• Involvement of the FAD Coenzyme in the Oxidative Deamination of Biogenic Amines

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