Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Chemistry of Conjugated Proteins
Metalloproteins

Metalloproteins are Biopolymers that contain, In addition to a protein moiety, one or more Metal Ions (Table 2.5). These Proteins include, for example, Non-heme iron proteins, as well as proteins coordinated with metal atoms within complex enzyme systems.

Typical Representatives of the former group are the iron-containing proteins ferritin, transferrin, and hemosiderin. Ferritin is a high-molecular-weight, Water-soluble protein with a Molecular Weight of 400,000, in which the iron content ranges from 17% to 23% (averaging 20%). It is concentrated mainly in the Spleen, Liver, and Bone Marrow, serving as an iron storage depot in the body. Iron in ferritin is present in an oxidized form as part of an inorganic iron-containing compound (FeO ∙ OH)₈∙ (FeO ∙ O ∙ PO₃H₂), where the chains of the inorganic polymer O=Fe—OH...O=Fe—OH..., sometimes containing phosphates, are located between the peptide chains of the protein portion (known as apoferritin), and the iron atoms are coordinatively bound to the nitrogen atoms of the peptide groups.

Transferrin is a water-soluble iron protein (molecular weight 90,000), a glycoprotein found primarily in Blood serum as a component of ß-globulins. Its iron content is 0.13%. It is hypothesized that the iron atom binds to the protein via coordination bonds involving the hydroxyl groups of Tyrosine. The transferrin molecule contains 2 iron atoms; transferrin acts as the physiological transporter of iron in the body.

Class="center">Table 2.5. Metalloproteins

Unlike ferritin and transferrin, hemosiderin is a water-insoluble iron-protein complex that also contains 25% NUCLEOTIDES and CARBOHYDRATES. It is found predominantly in the reticuloendothelial Cells of The Liver and spleen. The Biological Role of hemosiderin is not yet fully understood.

The second group of metalloproteins includes A number of enzymes: metalloenzymes, which contain metal ions tightly bound to the protein molecule and essential for their function (the metals remain bound to the enzymes throughout the purification process); and metal-ion-activated enzymes, which bind metals less firmly but require The addition of a specific metal to the reaction medium to exhibit activity. It is assumed that the mechanisms by which the metal participates in catalysis are most likely similar in both cases; metal ions are involved in The formation of a ternary complex: enzyme active center–metal–substrate (E—M—S), or M—E—S, or E—S—M. There is evidence that in the active center of many enzymes, the imidazole group of Histidine is involved in metal binding.