BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 2. THE ROLE OF WATER, MACRO- AND MICROELEMENTS IN THE VITAL ACTIVITY OF ORGANISMS

2.4. Macro- and microelements

Inorganic substances essential for the vital activity of an Organism can be divided into two groups: macro- and microelements. This division is somewhat arbitrary, although it is based on quantitative values. If the mass fraction of an element in an organism exceeds 10^-2 %, it is classified as a macroelement. The fraction of microelements in an organism ranges from 10^-3 to 10^-5 %. If an element's fraction is below 10^-5 %, it is referred to as an ultramicroelement.

All inorganic elements (Table 2.2) are required by any organism. Without a sufficient amount of them, basic physicochemical and biochemical processes, as well as the organism's responses to external stimuli, cannot take place. This is because macroelements (Ca and P) are constituents of bones (Ca₁₀(PO₄)₆(OH)₂), chlorine (Cl) is a component of Hydrochloric acid in gastric juice, and Na and K, located on opposite sides of Cell/30.html">The Plasma Membrane, ensure the Generation and Conduction of electrical potentials. Microelements are components of accessory substances—respiratory pigments, Vitamins, Hormones, Enzymes, and Coenzymes—that participate in The regulation of vital processes, influencing not only enzyme activity but also the direction of their action, which is why microelements are often called "catalysts of catalysts."

Microelements are required by organisms only in optimal amounts. Both their deficiency and excess in nutrients cause diseases and the death of organisms due to Metabolic Disorders. Microelements participate in such vital biochemical processes as Respiration (copper, zinc, manganese, cobalt), Photosynthesis (mananese, copper), Protein Synthesis (manganese, cobalt, copper, nickel, chromium), hematopoiesis (cobalt, copper, manganese, nickel, zinc), protein, carbohydrate, and Lipid METABOLISM (molybdenum, vanadium, cobalt, tungsten, manganese, zinc), etc. A characteristic feature of an essential element is the bell-shaped dose (n) versus response (R) curve, as illustrated in Fig. 2.7.

Most microelements are metals, more than half of which are transition metals (d-elements). Transition elements are defined as those in which the d- and f-atomic orbitals are filled with electrons in neutral free atoms. In the organism, they form coordination compounds with Biomolecules. For instance, manganese is a constituent of 12 enzymes, iron of 30, copper of 30, and zinc of over 100 enzymes.

Class="center">Table 2.2

Daily requirement of chemical elements in The Human Body and characteristic symptoms of their deficiency

Fig. 2.7. Dependence of the biological system's response (R) on the dose (n) of an essential (A) and toxic (B) element:

1 - basic response; 2 - reaction norm; 3 - Toxic Effect of the element

A significant portion of chemical elements are poisons to living organisms (Table 2.3). With the exception of beryllium and barium, these elements form stable sulfide compounds. The Mechanism of their toxic action is associated with the blockage of certain functional groups (including sulfhydryl groups) of Proteins, or the substitution of "beneficial" microelements in enzymes (Table 2.3). As can be seen from Fig. 2.7, up to a certain concentration of these elements, the organism seems unaffected by their harmful action. At high concentrations, they become poisons. This indicates that the concentration of any element in the organism plays a crucial role, no less significant than the type of element itself.

Table 2.3

Distribution of toxic elements across periods and groups of the Periodic Table

The human body (70 kg) contains: Ca 1700 g (including 1050 g in bones), K - 250 g, Na - 70 g, Mg - 42 g, Fe - 5 g, Zn - 3 g, Cu - 10 mg, Mn - 20 mg, Co - 5 mg, Cr - 5 mg. Among metalloids, P predominate with 700 g, S with 175 g, and Cl with 105 g. However, the ionic composition of body Tissues and fluids varies widely. The Blood of marine animals is close to seawater in its content of Na, K, Ca, Mg, and Cl. The blood of freshwater and terrestrial organisms contains 10 times less K and Na, and several times less Ca and Mg. At the same time, due to the selective permeability of Plasma Membranes and ion accumulation, Cells are rich in K and Mg, but low in Na and Ca. Certain species selectively accumulate specific elements. For instance, clubmosses accumulate Al, some Bacteria - Fe, tobacco - Zn, corn - Au and Zn, fly agaric mushrooms - vanadium, and all legumes - molybdenum, vanadium, etc. Hair and Nails accumulate Al, As, I, and V; Kidneys - Cd, Hg, and Mn; intestinal tissues - Sn; the Prostate Gland - Zn and Sr; the Brain - Cu, and the eye mucosa - barium. Even an element like silicon is a component of skin, Cartilage, and ligaments (up to 0.01 %), as well as mucopolysaccharides (dermatan and heparan sulfates (~0.04 %)), forming ester bonds such as

which act as bridges between polypeptide chains, etc.

Based solely on the fact that the content of transition metals in organisms is negligible, one can assume that their function must be related to catalysis. In addition, transition metals can perform (along with biomolecules) other Functions as well—they can transfer electrons, atomic groups, and entire molecules, fix molecules in a specific orientation, rotate them, polarize them, etc. For

example, Zn ions are essential components for hundreds of enzymes. They are present in dehydrogenases, which catalyze The transfer of hydride ions from substrate molecules to NAD and NADP coenzymes (nicotinamide adenine dinucleotide (phosphate)). Thus, liver Alcohol dehydrogenase, which dehydrogenates alcohol to acetaldehyde, contains two Zn ions that bind the NAD coenzyme to the enzyme's Active Site. Therefore, zinc deficiency contributes to Alcohol poisoning in the body. Zinc is also a component of DNA and mRNA polymerases, which participate in the Replication and Transcription of Genetic information. Among the most fascinating functions of zinc is The formation of a complex with Insulin and its involvement in taste and smell perception by Tongue and Nasal cavity receptors. The Effect of an inorganic ion on a biochemical reaction can also be caused by a strong electric field effect.

Iron (Fe) deficiency in the human body leads to anemia, as this metal ion is a component of blood Hemoglobin. The Link Between anemia and iron deficiency has been known for a long time (in the 17th century, anemia was treated with red wine infused with iron). However, an excess of iron causes siderosis of the eyes and Lungs—a disease caused by the deposition of iron compounds in the tissues of these Organs. Some metals are capable of reversible Oxidation and reduction. Due to this property, Fe, Cu, and Co are constituents of the active centers of many enzymes that catalyze redox processes. An example is cytochrome c oxidase, which catalyzes the reduction of molecular oxygen to Water using electrons derived from nutrient molecules. In the enzyme molecule, As a result of valence changes, iron reversibly transitions from the ferric form to the ferrous form (Fe³⁺↔Fe²⁺). This results in Electron transfer from cytochrome c to molecular oxygen. Copper atoms in the same cytochrome c oxidase also participate in electron transfer through cyclic valence changes, with oxygen serving as the electron acceptor. Copper deficiency is associated with dieback in trees and movement coordination disorders—ataxia in sheep and cattle. Its deficiency leads to blood vessel destruction, pathological bone growth, and Connective Tissue defects. The latter is explained by the fact that copper is part of the active center of lysyl oxidase, an enzyme that "cross-links" Collagen polypeptide chains using Lysine. In small concentrations, copper is used as an astringent and bacteriostatic agent (inhibiting bacterial reproduction), in the Treatment of Conjunctivitis in the form of eye drops, and as a caustic agent for trachoma in the form of eye pencils (an alloy of Cu²⁺, potassium nitrate, alums, and camphor); a 5 % copper sulfate solution is used to treat phosphorus Burns. At the same time, an excess of copper causes mental disorders and leads to paralysis of certain organs (Wilson's disease). Copper and zinc deficiency is a cause of anemia (copper is required for iron assimilation), while an excess of zinc alone in plants causes rosette disease in fruit trees and parakeratosis (skin thickening) in animals. An excess of strontium (Sr) in the soil causes malformed plant shapes, etc. When calcium is bound by calmodulin—a calcium-binding protein found in all animal, human, and plant cells—its conformation changes significantly. In this conformation, calmodulin (or rather, the complex of the protein with 1, 2, 3, and 4 Ca atoms) can bind to target enzymes and, as a result, alter their activity.

Enzymes whose activity depends on the presence of metals in their molecules are called metalloenzymes; more than 200 of them are known. In addition, microelements are components of vitamins (Co - B₁₂), hormones (I - thyroxine, Zn, Co - insulin), respiratory pigments (Fe - hemoglobin, Cu - hemocyanin), etc. The action of microelements is exerted through their influence on metabolism and, consequently, on physiological processes. These include growth (Mn, Zn, I - in animals; B, Mn, Zn, Cu - in plants), reproduction (Mn, Zn - in animals; Mn, Cu, Mo - in plants), hematopoiesis (Fe, Cu, Co), tissue respiration (Cu, Zn), etc. The effects of a single microelement often depend on the adequate content of others. For example, the uptake of molecular nitrogen by legumes is controlled by Mo, Co, and V. Cobalt acts effectively on hematopoiesis in the presence of Fe and Cu, manganese enhances Cu assimilation; at the same time, copper acts as an antagonist to Mo, F, Sr, etc., in certain effects.

Medicinal properties are also characteristic of metals classified among harmful chemical elements. Thus, the bactericidal (bacteria-killing) properties of silver and its salts have long been noticed. In medicine, a colloidal silver solution (collargol) is used to rinse purulent wounds, the Urinary Bladder in chronic cystitis and urethritis, and as eye drops for purulent conjunctivitis. Pencils of low silver nitrate concentration (0.10-0.25 %) are used as an astringent antimicrobial agent for compresses and as eye drops. It is believed that the caustic action of silver nitrate is associated with its interaction with proteins, resulting in the formation of silver protein salts—albuminates.

Thus, living organisms have rather strict requirements regarding specific concentrations of Trace Elements in their environment, their composition, forms, and mutual ratios. A deficiency or excess of trace elements in soils and water is equally detrimental to The Development of organisms, as it causes endemic diseases in plants, animals, and humans. Mineral Substances and inorganic ions, much like vitamins, often function not only as charge carriers, but also act as coenzymes in catalyzing the continuous Chemical Reactions taking place within The Cell. In living organisms, Metal Ions exist not only in a free state, but also as coordination compounds with biomolecules that act as ligands.

A. P. Vinogradov introduced THE CONCEPT OF biogeochemical provinces, defining them as "areas of the Earth within which organisms exhibit a biological reaction to a specific level of chemical elements in the environment." Numerous studies have established that in certain Regions of the Earth, deviations occur in PHYSIOLOGICAL AND BIOCHEMICAL reactions caused by either a deficiency or an excess of chemical elements for a given species or population due to natural or anthropogenic factors. For instance, endemic goiter has long been associated with insufficient iodine intake through nutrients, as it is strongly bound to humic substances in the soil. The action of cobalt, manganese, lead, and other elements can either impair or promote iodine assimilation. A deficiency of fluorine and molybdenum in soils and water leads to dental caries in humans, whereas an excess causes fluorosis. Excessive molybdenum intake through food (in ore-bearing mineral regions) results in endemic Gout or molybdenum toxicosis, among other conditions.

Biomedical research indicates that endemic diseases are not the only ones with territorial patterns of distribution. Atherosclerosis, gastrointestinal, cardiovascular, and endocrine disorders, Diabetes Mellitus, and Joint Diseases are also spatially restricted. Among non-communicable diseases, urolithiasis (Kidney stone disease) is most frequently linked to The chemical composition of specific objects or Components of the biosphere; among cardiovascular diseases, atherosclerosis and cardiosclerosis, and less commonly ischemic Heart disease; among gastrointestinal diseases, colitis and ulcers; and among liver diseases, cholecystitis, and so forth. There are three reasons for this: deficiency, excess, and imbalance of chemical elements throughout the entire biogeochemical chain.

Chromium, cobalt, copper, iodine, manganese, molybdenum, nickel, vanadium, and zinc are involved in the development of cardiovascular diseases. The highest mortality rates from these conditions are observed in areas with a general deficiency of trace elements, which is associated with podzolic soils. Excesses of chromium, cobalt, nickel, zinc, and cadmium in soils, water, and food products increase the incidence of Stomach and esophageal Cancer among the population. Lung Cancer is associated with living on mildly acidic soils depleted of iron, cobalt, and nickel. While zinc deficiency leads to dwarfism, delayed puberty, skin and mucous membrane lesions, dermatitis, and alopecia, its excess causes anemia. Lithium deficiency contributes to manic-depressive psychosis, Schizophrenia, and other mental disorders. In general, the more unfavorable the biogeochemical parameters of the environment, including the radiation Background, the earlier a particular human disease manifests and the more severe its course.

Soils serve as a habitat for microorganisms, including bacteria, Molds, and Viruses. The levels of chemical elements in soils can affect the vital activity of pathogens or the living conditions of their hosts and vectors. For example, evidence exists regarding The Role of biogeochemical factors in the natural foci of plague and tick-borne encephalitis. Foci of rabies among animals are associated with soils having a reduced content of titanium, nickel, and zirconium. Conversely, foci of anthrax are activated in soils with a high titanium content. Leptospirosis in animals is most frequently recorded on soils deficient in all trace elements except titanium and zirconium. This means that the specific trace element composition of soils can be used to indicate areas with a potentially elevated prevalence of infectious foci.

Thus, The activity of biological systems depends on the presence of inorganic ions within the system. They are primarily required to regulate enzyme activity, including redox enzymes. The active centers of such enzymes incorporate metals capable of reversible oxidation and reduction. Of equal importance is the ability of metal ions to influence the orientation of macromolecular segments, leading to conformational changes. Metal ions perform all their functions both in a free state and as coordination compounds with biomolecules acting as ligands.