Biochemical Foundations of Human Vital Activity - Volkov, N. I., & Nesen, E. N. 2000

Biochemical Foundations of Human Vital Activity
Vitamins
Characteristics of Water-Soluble Vitamins

The molecules of Water-Soluble Vitamins contain hydrophilic groups (-NH₂; -OH; -COOH, etc.) that facilitate their high solubility in water. Consequently, they are easily absorbed into the bloodstream from the intestines, while any excess is rapidly excreted in the urine, preventing The Development of hypervitaminosis. Because these vitamins do not accumulate in The Human Body and their absence in the diet quickly leads to hypovitaminosis or avitaminosis, they must be regularly ingested in specific amounts (Table 10). Water-soluble vitamins are notable for their thermolability and stability in acidic environments. Many of them act as Cofactors in various Enzymes that regulate METABOLISM. For example, five B-complex vitamins and Vitamin C are involved in regulating the aerobic oxidation of CARBOHYDRATES (Fig. 44).

Class="center">TABLE 10 Daily requirement of water-soluble vitamins for adults and their dietary sources

Fig. 44 Participation of water-soluble vitamins in the REGULATION OF CARBOHYDRATE oxidation in skeletal Muscles

Vitamin B₁

Biological role. Vitamin B₁ (thiamine) is involved in regulating Carbohydrate Metabolism as a component of enzymes that accelerate The conversion of pyruvic acid into acetyl-CoA, the primary intermediate in the aerobic oxidation of carbohydrates and other substances. This vitamin is also part of the enzymes involved in the Biosynthesis of Nucleic acids, as well as The Citric Acid Cycle enzymes that enhance ATP production, particularly in Nerve Cells.

Avitaminosis is associated with the accumulation of pyruvic acid in the body, which, in large quantities, alters the acid-base balance and disrupts the Functions of the central and peripheral nervous systems, as well as impairs acetylcholine synthesis due to decreased ATP formation. As a result, a Nervous system disorder known as polyneuritis (beriberi) develops—a progressive degeneration of nerves characterized by loss of Skin sensitivity, impaired secretory and motor functions of the gastrointestinal tract, and Muscle paralysis followed by atrophy.

Hypovitaminosis of thiamine is characterized by the accumulation of carbohydrate metabolic products (pyruvic and lactic acids) in the body, which alters the acid-base balance, suppresses gastric secretion, reduces the body's resistance to infections, and causes irritability and general weakness.

During physical activity, the daily requirement for Vitamin B1 increases to 6–8 mg due to its involvement in regulating aerobic energy production processes, especially in endurance sports.

Chemical Structure. Vitamin B₁ is a heterocyclic compound containing pyrimidine and thiazole rings. It includes an amino group (NH₂) and sulfur (S), which is why it is called thiamine:

Vitamin B₁ was the first vitamin to be obtained in pure form in a laboratory by C. Funk in 1911.

Vitamin B₂

Biological role. Vitamin B₂ (riboflavin) is involved in aerobic energy production (tissue Respiration) because it is a component of Flavin Coenzymes FAD and FMN, which function as hydrogen carriers. Additionally, it regulates amino acid conversion and Protein Biosynthesis, thereby stimulating growth processes.

Avitaminosis manifests as inflammation of the oral mucosa, visual disturbances, growth retardation, and specific dermatitis. Neurologically, avitaminosis is characterized by convulsions and paralysis.

Hypovitaminosis manifests as alterations in the mucous membrane of the Lips and Tongue, peeling, cracking of the lips, decreased night Vision, headaches, muscle cramps, and weakness.

Chemical structure. Vitamin B₂ is a derivative of isoalloxazine and the alcohol ribitol:

The requirement for vitamin B₂ increases under conditions of inadequate protein intake, Hypoxia, and intense physical activity associated with a significant increase in aerobic energy production.

Vitamin B₃

Biological role. Vitamin B₃ (pantothenic acid) is a component of the Acetylation coenzyme—coenzyme A, which participates in the aerobic oxidation of carbohydrates, fats, and Proteins, meaning it regulates Energy Metabolism. It is also involved in the synthesis of Fatty acids, proteins, acetylcholine, and Adrenocortical Hormones.

Avitaminosis is not observed in healthy individuals because the requirement for vitamin B₃ is met by the intestinal microflora.

Hypovitaminosis manifests as dermatitis, weight loss, Hair loss and graying, motor incoordination ("goose-stepping gait"), and paralysis.

Chemical structure. Vitamin B₃ consists of pantoic acid and Alanine linked by a peptide bond:

Vitamin B₆

Biological Role. Vitamin B₆ (pyridoxine) is involved in regulating Amino acid metabolism and Protein Synthesis, exhibiting an anabolic effect. It also regulates Lipid Metabolism by enhancing the absorption of Unsaturated fatty acids. This vitamin is a component of the enzyme phosphorylase, which accelerates Glycogen breakdown in Tissues, helps increase creatine levels in muscles, and influences The production of serotonin, histamine, and GABA—compounds that play a key role in regulating Muscle contraction and nervous system functions.

Avitaminosis is rare since this vitamin is partially synthesized by the microflora of the Large Intestine. However, prolonged antibiotic use can lead to vitamin deficiency, which manifests as dermatitis, a reduced red Blood Cell count, stunted growth, and nervous system disorders.

Hypovitaminosis manifests as loss of appetite, a decreased lymphocyte count in the blood, memory impairment, and dermatitis.

Chemical Structure. Vitamin B₆ is a pyrimidine derivative and can exist in three forms—pyridoxine, pyridoxal, and pyridoxamine:

In the body, all of these forms are converted into Pyridoxal phosphate, which carries out the biological function of vitamin B₆.

Vitamin B₁₂

Biological Role. Vitamin B₁₂ (cyanocobalamin) participates in nucleic acid synthesis and amino acid transformations, thereby activating protein synthesis, growth, and tissue repair—in other words, exhibiting a potent anabolic effect. It increases red blood cell counts and prevents fatty liver infiltration (lipotropic effect), while also improving Methionine Metabolism and influencing the Biological Oxidation processes of pyruvic and acetic acids.

Avitaminosis manifests as pernicious anemia, symptoms of which include a sharp drop in red blood cell counts, decreased Hemoglobin levels, and the appearance of immature Blood Cells. This condition is associated with impaired production of Hydrochloric acid and the protein transcobalamin in the gastric mucosa, which is necessary for the absorption of vitamin B₁₂ into the bloodstream.

Chemical Structure. Vitamin B₁₂ has a complex structure similar to hemoglobin. It contains 4 pyrrole rings linked not by an iron atom, as in hemoglobin, but by a cobalt (Co) atom:

A deficiency of any B-complex vitamins in athletes negatively affects muscular performance, as these vitamins regulate energy production and protein biosynthesis processes, which ensure rapid recovery and adaptation. However, an excess of these vitamins in the body does not lead to any additional boost in physical performance.

Vitamin H

Biological Role. Vitamin H (biotin) is involved in the metabolism of Higher Fatty Acids, nitrogenous bases, and Nucleic Acids, as well as in glucose biosynthesis. Therefore, it is essential for the proper functioning of muscles and The Nervous System.

Avitaminosis is uncommon because vitamin H is synthesized by intestinal microflora.

Hypovitaminosis may develop upon consuming large amounts of raw chicken eggs, which contain the protein Avidin. Avidin binds biotin in the gastrointestinal tract, forming a water-insoluble complex and rendering it unavailable for absorption. Biotin deficiency is manifested by skin flaking, muscle pain, anemia, reduced working capacity, and seborrhea (hypersecretion of the Sebaceous Glands).

Chemical Structure. Vitamin H is a derivative of monocarboxylic valeric acid, thiophene, and a cyclic form of urea:

Biotin (from the Greek bios — life) was first isolated in 1935 from egg yolk. Obtaining 1 g of biotin required 225 kg of dried egg yolk.

Vitamin C

Biological Role. Vitamin C (ascorbic acid) is involved in redox reactions and hydrogen transfer during aerobic energy production. It influences the synthesis of Collagen, a protein that helps maintain the structural integrity of supporting tissues (Cartilage and bone) and ensures normal vascular wall permeability. The activity of many enzymes depends on the presence of ascorbic acid. Primarily, this applies to enzymes involved in Amino Acid and NUCLEIC ACID METABOLISM, as well as muscle protein biosynthesis, which dictates the anabolic action of vitamin C. This vitamin stimulates hematopoiesis by improving iron absorption from the gut, and enhances liver protective functions, thereby increasing the body's resistance to various toxins and promoting faster recovery after intense physical exertion. Vitamin C affects the synthesis of Adrenal hormones, including corticosteroids, which improves the body's adaptive responses and enhances its resistance to infections and colds. Due to these biological functions, it is widely used in medicine and sports.

Human avitaminosis manifests as a severe disease known as scurvy (scorbutus). Scurvy increases the permeability of Blood Vessels, especially capillaries, leading to hemorrhages and bleeding. This is linked to impaired synthesis of collagen, which gives strength to vascular walls. The condition is typically characterized by gum damage, petechial skin hemorrhages, and damage to bones and Teeth in particular. To prevent scurvy, a mere 10 mg of ascorbic acid per day is sufficient, although a therapeutic dose of 200–300 mg ∙ day^-1 is administered. Nevertheless, recent data indicate that taking synthetic supplements of this vitamin in amounts exceeding 60 mg promotes The formation of toxic compounds in tissues.

Hypovitaminosis leads to a reduced resistance of the body to various infectious diseases, as well as a decrease in the secretory and motor functions of the gastrointestinal tract and respiratory Organs, the onset of dental caries, bleeding Gums, and rapid fatigue. Such a state arises not only from inadequate Dietary intake of the vitamin, but also from environmental chemical pollution, high physical loads, emotional stress, and periods of intensive growth in childhood.

The requirement for ascorbic acid increases under conditions of high and low ambient temperatures, as well as during intense mental and physical stress, such as in athletes during competitive periods.

Chemical structure. Vitamin C is an unsaturated hexose. Under the action of enzymes, it is easily oxidized (losing hydrogen) and converted into dehydroascorbic acid, which, upon attaching hydrogen atoms, is converted back into ascorbic acid:

Thus, vitamin C participates in the redox reactions of tissue respiration. The oxidation of ascorbic acid to dehydroascorbic acid protects it from degradation and elimination from the body. This process is enhanced by the action of Vitamin P.

Ascorbic acid is widely used for the Prevention and Treatment of many diseases, as well as for maintaining high physical performance. However, it should be kept in mind that large doses of vitamin C can cause Bone tissue disorders (Osteoporosis) and reproductive dysfunction, promote thrombosis, or even lead to malignant tissue transformation.

Vitamin P

Biological effects. Vitamin P (rutin), like other substances with P-vitamin activity (citrin, hesperidin, eriodictyol, catechins), participates in redox reactions and stimulates tissue respiration, as well as regulates capillary permeability. This action of vitamin P is closely interrelated with vitamin C, which led to the creation of their complexes (ascorutin and galascorbin). These preparations improve the condition of blood vessel walls, regulate the acid-forming function of The Stomach, Bile secretion processes, and The rate of recovery reactions in the body.

Avitaminosis is practically non-existent, whereas hypovitaminosis may occur due to impaired intestinal absorption of this vitamin and manifests as petechial rash (small hemorrhages around the hair follicle), leg pain, weakness, and rapid fatigue.

Chemical structure. Vitamin P is a yellow-orange flavine derivative of glucosides:

Vitamin P was first isolated from lemon peel in 1936 by the Hungarian biochemist A. Szent-Györgyi.

Vitamin PP (Vitamin B₅)

Biological effects. Vitamin PP (nicotinic acid) participates in redox reactions as an integral component of the coenzymes NAD and NADP, which act as hydrogen atom carriers. These coenzymes are involved in the anaerobic and aerobic oxidation of carbohydrates, hepatic glycogen formation, Fatty acid and phospholipid synthesis, and amino acid metabolism, while also normalizing blood Cholesterol levels. In the body, PP is partially synthesized from the essential amino acid Tryptophan (provitamin PP).

Avitaminosis leads to impaired formation of dehydrogenase coenzymes that catalyze tissue respiration processes, and to the development of a disease known as pellagra ("rough skin"). Pellagra is the disease of the three "Ds": dermatitis, diarrhea, and dementia (mental deterioration manifested by memory loss, hallucinations, and delusions). Cardiac dysfunction is also observed. The disease develops in cases of inadequate protein Nutrition (insufficient intake of The amino acid tryptophan, found in meat) and a deficiency of vitamin B₆, which is necessary for the synthesis of vitamin PP.

Hypovitaminosis causes brownish skin pigmentation, predominantly on exposed areas of the body, keratinization and peeling of the skin, as well as psychiatric disorders such as irritability and apathy.

Chemical structure. Vitamin PP is a pyridine derivative and can be represented by nicotinic acid (a) and nicotinamide (b):

The biological activity of both compounds is practically identical. Nicotinic acid is resistant to heat, atmospheric oxygen, light, and acidic or alkaline environments.

Vitamin B_c

Biological effects. Vitamin B_c (folic acid) participates in amino acid and nucleic acid metabolism, which is associated with enhanced protein synthesis (anabolic effect). Folic acid promotes the absorption of vitamin B₁₂, thereby boosting hematopoiesis and exerting an anti-anemic effect. It has The ability to bind hydrogen, which determines its participation in redox processes related to energy production.

Avitaminosis is associated with impaired nucleic acid synthesis and hematopoiesis, leading to a decrease in hemoglobin levels (anemia and leukopenia).

Hypovitaminosis manifests as bleeding of the oral mucous membranes and gums, gastrointestinal disorders, fatty liver infiltration, and the development of dermatitis and stomatitis.

Chemical structure. The molecule of vitamin B_c is composed of glutamic acid, Para-aminobenzoic Acid, and pteridine:

Folic acid was first isolated from spinach leaves, from which it derived its name (Latin folium — leaf). In the human body, folic acid is converted into tetrahydrofolic acid, which exhibits biological activity.