Biochemistry

(oxymyoglobin, carboxymyoglobin and metmyoglobin). The molecular weight of the protein component of myoglobin, which has a crystalline appearance, is 17,000. Each molecule contains one heme molecule. Myoglobin is considered as a respiratory pigment that provides the muscles with a short-term supply of oxygen used by muscle fibers. Myoglobin affinity for oxygen is more pronounced than for hemoglobin. Particularly important is the role of myoglobin in the life of aquatic animals. In humans, with a total oxygen supply of 2,450 ml, 345 ml (i.e. 14%) is in the form of oxymyoglobin. Myoglobin, providing a reserve of oxygen in the muscles, protects the organs of animals from temporary oxygen starvation. Of particular importance in this regard should be myoglobin of the heart muscle. Other iron chromoproteins. Chromoproteins containing iron porphyrin (heme) are present in nature not only by hemoglobins and myoglobins. The catalase enzyme, which has four hemes in its molecule, is very common in the tissues of animals and some bacteria. In plant organisms, another heme-containing enzyme, peroxidase, is widespread. This enzyme is also found in animal tissues. Catalase and peroxidase are oxidative enzymes. Heme is also found in other substances of a chromoprotein nature - cytochromes. The latter are found in all cells that consume oxygen and, therefore, are widespread in the organic world. Cytochromes are involved in processes leading to the use of oxygen by cells. Among the cytochromes isolated from cells ( “ a ” , “ b ” and “ c” ), the most studied is cytochrome “ c ” , obtained in crystalline form (molecular weight 13,000, one heme molecule). The heme is bound to the protein component of cytochrome “ c" by one main bond, going from iron to histidine, and two covalent bonds between the heme vinyl groups and the globin cysteine residues. When studying iron-containing chromoproteins, the very wide use of protoporphyrin structure in nature for the formation of biologically important substances is noteworthy. It also find protoporphyrin in chlorophyll, which is one of the most important organic compounds of plants. In the chlorophyll molecule, as in the heme molecule, there are four pyrrole nuclei connected to each other, which bind the magnesium atom with two main and two additional valencies. Chlorophyll along with this is an ester of two basic acids and two alcohols - methyl and phytol (high molecular weight unsaturated alcohol). Flavoproteins. Flavoproteins include proteins that are colored yellow. Color depends on the presence of flavin adenine nucleotide in them as a prosthetic group. Flavoproteins are widespread and they play the role of enzymes. Nucleoproteins. Proteins associated with nucleic acids. They are part of any cell and play an important biological role, participating in the formation of structural cellular elements and the transmission of hereditary information. (Л