Hemoglobin carbon dioxide

Figure 6-9. The Bohr effect. Carbon dioxide generated in peripheral tissues combines with water to form carbonic acid, which dissociates into protons and bicarbonate ions. Deoxyhemoglobin acts as a buffer by binding protons and delivering them to the lungs. In the lungs, the uptake of oxygen by hemoglobin releases protons that combine with bicarbonate ion, forming carbonic acid, which when dehydrated by carbonic anhydrase becomes carbon dioxide, which then is exhaled.

The major functions of the red blood ceil are relatively simple, consisting of dehvering oxygen to the tissues and of helping in the disposal of carbon dioxide and protons formed by tissue metabolism. Thus, it has a much simpler structure than most human cells, being essentially composed of a membrane surrounding a solution of hemoglobin (this protein forms about 95% of the intracellular protein of the red cell). There are no... 

Carbon dioxide can combine chemically with the terminal amine groups (NH2) in blood proteins. The most important of these proteins for this process is hemoglobin. The combination of carbon dioxide and hemoglobin forms carbamino hemoglobin ... 

Deoxyhemoglobin can bind more carbon dioxide than oxygenated hemoglobin. Therefore, unloading of oxygen in the tissues facilitates loading... 

This entire reaction is reversed when the blood reaches the lungs. Because carbon dioxide is eliminated by ventilation, the reaction is pulled to the left. Bicarbonate ions diffuse back into the red blood cells. The hemoglobin releases the hydrogen ions and is now available to load up with oxygen. The bicarbonate ions combine with the hydrogen ions to form carbonic acid, which then dissociates into carbon dioxide and water. The carbon dioxide diffuses down its concentration gradient from the blood into the alveoli and is exhaled. A summary of the three mechanisms by which carbon dioxide is transported in the blood is illustrated in Figure 17.8. 

Decreasing pH and increasing CO2 concentration lower hemoglobin s O2 affinity so that conditions of low pH and high carbon dioxide concentration promote... 

The blood is made up of a liquid portion called the plasma and a solid portion which in turn comprises both red cells and white cells. The red cells, which are formed in the bone marrow and then passed into the blood stream, contain a chemical called hemoglobin that has the capacity to carry oxygen to the body tissues and carbon dioxide away from the body tissues. The white cells are involved in maintaining immunity to infection and in fighting disease. It is the interference by a virus with the immume process of the white cells that give rise to what we know as AIDS (auto immune deficiency syndrome). This condition, however, does not occur from exposure to chemicals. 

Protein functions and interactions are infinitely varied in biological species— one of the major problems associated with complete classification of any proteome. Proteins may transport substances myoglobin and hemoglobin (discussed in Chapter 7) transport oxygen, and carbon dioxide, in mammalian blood. Proteins called enzymes catalyze necessary biochemical reactions. The active site of an enzyme contains those amino acids that come in direct contact... 

Transport. A wellknown transport protein is hemoglobin in the erythrocytes (bottom left). It is responsible for the transport of oxygen and carbon dioxide between the lungs and tissues (see p.282). The blood plasma also contains many other proteins with transport functions. Prealbumin (transthyretin middle), for example, transports the thyroid hormones thyroxin and triiodothyronine. Ion channels and other integral membrane proteins (see p.220) facilitate the transport of ions and metabolites across biological membranes. 

The most important task of the red blood cells (erythrocytes) is to transport molecular oxygen (O2) from the lungs into the tissues, and carbon dioxide (CO2) from the tissues back into the lungs. To achieve this, the higher organisms require a special transport system, since O2 is poorly soluble in water. For example, only around 3.2 mb O2 is soluble in 1 L blood plasma. By contrast, the protein hemoglobin (Hb), contained in the erythrocytes, can bind a maximum of 220 mb O2 per liter—70 times the physically soluble amount. 

Hemoglobin is also decisively involved in the transport of carbon dioxide (CO2) from the tissues to the lungs. 

Brydon and Roberts- added hemolyzed blood to unhemolyzed plasma, analyzed the specimens for a variety of constituents and then compared the values with those in the unhemolyzed plasma (B28). The following procedures were considered unaffected by hemolysis (up to 1 g/100 ml hemoglobin) urea (diacetyl monoxime) carbon dioxide content (phe-nolphthalein complex) iron binding capacity cholesterol (ferric chloride) creatinine (alkaline picrate) uric acid (phosphotungstate reduction) alkaline phosphatase (4-nitrophenyl phosphate) 5 -nucleotidase (adenosine monophosphate-nickel) and tartrate-labile acid phosphatase (phenyl phosphate). In Table 2 are shown those assays where increases were observed. The hemolysis used in these studies was equivalent to that produced by the breakdown of about 15 X 10 erythrocytes. In the bromocresol green albumin method it has been reported that for every 100 mg of hemoglobin/100 ml serum, the apparent albumin concentration is increased by 100 mg/100 ml (D12). Hemolysis releases some amino acids, such as histidine, into the plasma (Alb). 

Human carbonic anhydrase II, found primarily in the erythrocyte, is the prototypical member of the family of carbonic anhydrases and has been extensively reviewed (Pocker and Sarkanen, 1978 Lindskog, 1983, 1986 Silverman and Lindskog, 1988). Within the erythrocyte carbonic anhydrase II hydrates CO2 to form bicarbonate ion plus a proton via tandem chemical processes (Silverman and Lindskog, 1988) (Scheme 2). Most of the carbon dioxide generated during the process of respiration requires this carbonic anhydrase Il-catalyzed event for transport out of the cell. The resultant protons of CO2 hydration are taken up by His-146)8, His-122a, and the amino terminus of the a subunits of the hemoglobin tetramer. As a reference. Scheme 3 outlines the interconversions... 

Asphalt Hydrocarbon material ranging in consistency from heavy liquid to a solid. Most common source is residue left after fractional distillation of crude oils used primarily for surfacing roads. Asphyxia Suffocation from lack of oxygen. Chemical asphyxia is produced by a substance, such as carbon monoxide, that combines with hemoglobin to reduce die blood s capacity to transport oxygen. Simple asphyxia is the result of exposure to a substance, such as carbon dioxide, that displaces oxygen. 

This reaction is catalyzed by carbonic anhydrase, an enzyme particularly abundant in erythrocytes. Carbon dioxide is not very soluble in aqueous solution, and bubbles of C02 would form in the tissues and blood if it were not converted to bicarbonate. As you can see from the equation, the hydration of C02 results in an increase in the H+ concentration (a decrease in pH) in the tissues. The binding of oxygen by hemoglobin is profoundly influenced by pH and C02 concentration, so the interconversion of C02 and bicarbonate is of great importance to the regulation of oxygen binding and release in the blood. 

Binding of C02 Most of the carbon dioxide produced in metabolism is hydrated and transported as bicarbonate ion (see p. 9). However, some CO2 is carried as carbamate bound to the uncharged a-amino groups of hemoglobin (carbamino-hemo-globin see Figure 3.7), which can be represented schematically as follows ... 

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