Biochemistry

chemical structure it is the same in different vertebrates. Globins in the content of diaminomonocarboxylic acids in them belong to histones. The molecular weight of hemoglobin is 67-70 thousand and four molecules of heme are contained in its molecule. The heme molecule contains one iron atom. The nature of the joining of the heme to the globin has not yet been fully clarified. It is believed that it is carried out by a covalent bond between heme iron and globin histidine. The heme structure is based on pyrrole derivatives. Each molecule contains four pyrrole derivatives linked to each other by methine groups (-CH-) and one divalent iron atom. The skeleton of the heme molecule is porphin, which consists of four pyrrole derivatives connected to each other via methine bridges. When heme is cleaved by treating hemoglobin with acetic acid and sodium chloride, it oxidizes to form hemin. Globin - — Fe _ N N~' 4 ' Hemoglobin Globin ........... Fe — O 2 N -^N ''' Oxyhemoglobin N Globin - — Fe — CO 2 N N ''' Carbohemoglobin N Globin Carboxyhemoglobin The most interesting biological feature of a heme is its ability to combine with gases (oxygen, carbon monoxide, etc.). When oxygen is attached to hemoglobin (H B ), oxyhemoglobin (HgO^ is formed', O 2 joins the iron due to additional bonds. H B O 2 is so unstable that even with a decrease in the partial pressure of oxygen, it decomposes (dissociates) with the formation of H B and O 2 . The addition of O 2 to H B blood occurs in the lungs, but the decomposition of H B O 2 into H B and O 2 takes place in the blood flowing to the tissues, which is very important for supplying tissues with oxygen. When CO 2 is added to hemoglobin, carbhemoglobin is formed. It carries out the transfer of carbon dioxide from tissues to the lungs. Carbon monoxide (carbon monoxide) is easily attached to hemoglobin (the iron it contains) to form carboxyhemoglobin (H B CO). When inhaling the air in which CO is contained, the latter displaces O 2 from H B O 2 , taking its place. As a result, oxygen delivery from the lungs to the tissues is disrupted. An important hemoglobin derivative is methemoglobin, in the molecule of which the iron atom is trivalent. Methemoglobin is formed from H B O 2 when exposed to oxidizing agents K 3 Fe(CN)t, nitrogen oxides, methylene blue, etc. The formation of an inert, strongly binding oxygen methemoglobin in the blood reduces the amount of functionally important H B O 2 in it, disrupts the delivery of O 2 to tissues, which leads to serious pathological consequences. Myoglobin. A substance close to hemoglobin is muscle chromoprotein - myoglobin or muscle hemoglobin. Myoglobin is close to blood hemoglobin, but not identical to it. It forms the same derivatives as blood hemoglobin 66