Oxygen transport, by hemoglobin

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]. 

The cationic charge in blood is neutralized by two major anions, Cl and HC03. The chloride ion plays a role in acid-base balance, maintenance of osmotic pressure within an acceptable range, and oxygen transport by hemoglobin. The bicarbonate anion is the form in which most waste CO2 is carried in the blood. 

Immediately below, we note the historical case of oxygen transport by hemoglobin from lungs to the tissues and note how this would be discussed in terms of the consilient mechanism. This was the first biological system appreciated for its positive cooperativity, the cooperative binding of oxygen molecules that is key to successful transport. 

A key aspect of our consilient view of oxygen transport by hemoglobin, derived as it has been... 

In human and other mammalian populations, heme is the functional cofactor for critical diverse metabolic processes in the body such as oxygen transport by hemoglobin and myoglobin, the operation of various cytochromes in oxidative processes ranging from oxidative phosphorylation and detoxification of organic xenobiotics to enzymatically mediated formation of the hormonal form of vitamin D in kidney. 

Fig. 3. Oxygen transport by perfluorocarbons versus hemoglobin (Hb) (a) In the case of PFCs, O2 dissolution is characterized by loose, nondirectional van der Waals interactions. Oxygen solubility follows Henry s law, that is, is directly proportional to the gas s partial pressure (curve c). (b) In the case of Hb, a strong, localized chemical bond is established with the iron atom of a heme. Successive binding of four O2 molecules to the four hemes of Hb is cooperative, and saturation occurs when all four iron atoms are bound. Hence, the sigmoid shape of the O2 uptake curve, which levels off when the partial pressure of O2 on earth is attained (curve d) [20].

FIGURE 3-1 Some functions of proteins, (a) The light produced by fireflies is the result of a reaction involving the protein luciferin and ATP, catalyzed by the enzyme luciferase (see Box 13-2). (b) Erythrocytes contain large amounts of the oxygen-transporting protein hemoglobin. (c) The protein keratin, formed by all vertebrates, is the chief structural component of hair, scales, horn, wool, nails, and feath-... 

Nearly all the oxygen carried by whole blood in animals is bound and transported by hemoglobin in erythrocytes (red blood cells). Normal human erythrocytes are small (6 to 9 pm in diameter), biconcave disks. They are formed from precursor stem cells called hemocytoblasts. In... 

To begin, we will consider the principles of allostery by examining two proteins the enzyme aspartate transcarhamoylase and the oxygen-transporting protein hemoglobin. 

Over a century ago, hemoglobin (Hb), the protein in RBCs, was discovered to be the means of oxygen transport by bloodJ Thus, it is not surprising that preparations of this protein have been repeatedly evaluated as the active principal of temporary blood replacement solutionsJ ... 

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