Hemoglobin binding reactions

In addition to structure control, metal ions can act as reactive centers of proteins or enzymes. The metals can not only bind reaction partners, their special reactivity can induce chemical reaction of the substrate. Very often different redox states of the metal ions play a crucial role in the specific chemistry of the metal. Non-redox-active enzymes, e.g. some hydrolytic enzymes, often react as a result of their Lewis-acid activity [2], Binding of substrates is, however, important not only for their chemical modification but also for their transport. Oxygen transport by hemoglobin is an important example of this [3]. 

In 1909 A. V. Hill proposed that the binding reaction between hemoglobin (Hb) and oxygen could be described by a reaction of molecularity n + 1 ... 

An alternative way of viewing the concept of extrinsic binding constants is as follows. The experimentally measured binding constant for each site of a polymeric protein, or enzyme, will depend on the number of available sites on each molecule e.g., for the hemoglobin tetramer the first binding reaction is... 

Conformational changes are frequently invoked to describe biochemical mechanisms qualitatively. With the surface free energy model, it is possible to evaluate the energetic consequences of conformational changes in proteins. We have done this for the ligand-binding reactions of hemoglobin (8). 

Iron in the hemoglobin binds O. The chemical reaction equation for this binding is expressed as follows ... 

For reaction B, the binding of oxygen to hemoglobin, the reaction quotient is... 

Certain examples illustrate the importance of nonenzymatic binding reactions. These include hemoglobin, protein-phospholipid interactions, and the nonenzymatic binding abilities of proteins, nucleic acids, and mucopolysaccharides. 

AH of the reactions considered to be useful in the production of hemoglobin-based blood substitutes use chemical modification at one or more of the sites discussed above. Table 2 Hsts the different types of hemoglobin modifications with examples of the most common reactions for each. Differences in the reactions are determined by the dimensions and reactivity of the cross-linking reagents. Because the function of hemoglobin in binding and releasing... 

The oxygen affinity of the derivative was shown to be about half that of unmodified hemoglobin under similar conditions, but a degree of cooperativity was preserved. Kquilihrium and kinetic ligand-binding studies on this derivative have been interpreted (62) to show a perturbed R state. It is beheved that although the reaction is between the two P-chains, aP-dimers function independentiy, probably through a flexible connection. 

The most conspicuous use of iron in biological systems is in our blood, where the erythrocytes are filled with the oxygen-binding protein hemoglobin. The red color of blood is due to the iron atom bound to the heme group in hemoglobin. Similar heme-bound iron atoms are present in a number of proteins involved in electron-transfer reactions, notably cytochromes. A chemically more sophisticated use of iron is found in an enzyme, ribo nucleotide reductase, that catalyzes the conversion of ribonucleotides to deoxyribonucleotides, an important step in the synthesis of the building blocks of DNA. 

Hemoglobin (Hb) binds to both oxygen and carbon monoxide. When tiie carbon monoxide replaces the oxygen in an organism, the following reaction occurs ... 

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