Abstract
Metals have a wide range of effects on biological processes, playing an important role in maintaining the functioning of the human body. However, many metals, including essential elements, can have a toxic effect on the body, leading to pathological processes. The biological role of an element depends on a number of physicochemical facts, such as the oxidation degree and the formation of metal-ligand organic and inorganic complexes. For example, most of the iron binds to transferrin and ferritin ensuring the safe transportation of the fenton-active trivalent metal ions in the bloodstream. Free Fe3+ ions lead to the formation of reactive oxygen species and further damage of cell structures. Thus, the chemical form of the element determines the toxicokinetics and toxicodynamics of metals. Knowledge in total exposure of elements in biological fluids is not enough to understand the complex mechanism of biological and abnormal reactions. It is necessary to study the interaction of metal elements with various ligands such as high- and low-molecular compounds (proteins, polysaccharides, nucleic acids, citrates, amino acids). In this regard, the application of modern analytical methods is becoming increasingly important to obtain qualitative and quantitative data on elements, ionic forms, speciation and functions in biological systems. The combination of these methods is called speciation analysis, which is a well-established way to study the biological role and metabolism of trace elements. This article reviews the main metal-ligand forms of iron (transferrin, albumin, ferritin and citrate) and zinc (albumin, 2-macroglobulin, IgG, transcuprein, metallothioneins, ZIP and ZnT transporters). This information can be useful both in fundamental and applied researches in the biology and medicine.