Chloride shift

In the chloride shift, Ck plays an important role in the transport of carbon dioxide (qv). In the plasma, CO2 is present as HCO, produced in the erythrocytes from CO2. The diffusion of HCO requires the counterdiffusion of another anion to maintain electrical neutraUty. This function is performed by Ck which readily diffuses into and out of the erythrocytes (see Fig. 5). The carbonic anhydrase-mediated Ck—HCO exchange is also important for cellular de novo fatty acid synthesis and myelination in the brain (62). 

Figure 5.14 Chloride shift in a red cell (a) in a tissue capillary (b) in a pulmonary capillary...

Cleavage of the oxirane C-0 bond produces a zwitterionic intermediate (Fig. 10.22), which that can undergo chloride shift (Pathway a) to 2,2-dich-loroacetyl chloride (10.90) followed by hydrolysis to 2,2-dichloroacetic acid (10.91). Furthermore, the zwitterionic intermediate reacts with H20 or H30+ (Pathway b) by pH-independent or a H30+-dependent hydrolysis, respectively. The pH-independent pathway only is shown in Fig. 10.22, Pathway b, but the mechanism of the H30+-dependent hydrolysis is comparable. Hydration and loss of Cl, thus, leads to glyoxylyl chloride (10.92), a reactive acyl chloride that is detoxified by H20 to glyoxylic acid (10.93), breaks down to formic acid and carbon monoxide, or reacts with lysine residues to form adducts with proteins and cytochrome P450 [157], There is also evidence for reaction with phosphatidylethanolamine in the membrane. 

The chloride shift was originally detected as a markedly lower concentration of chloride in plasma from venous blood compared with that from arterial blood. 

Cupric sulfate exerts an effect on the silver chloride-hydroxylamine reaction similar in kind to that which it exerts on the hydrazine reaction, but in a smaller degree. If sufficient cupric sulfate is added to the hydroxylamine solution, the character of the reduction of silver chloride shifts towards that shown by the hydrazine reaction, e.g., the effect of gelatin becomes less pronounced, a minimum rate at a small gelatin addition is not obtained, and significant amounts of colloidal silver appear in the solution. 

CHLORIDE (Biological Aspects). Sodium chloride, potassium chloride, and other chloride salts, when ingested by animals from feedstuffs and humans from various food substances, reduce to a consideration of the cation involved (Na", K h. etc.) and the Cl (chloride) ion. Generally, in terms of animal and human nutrition, more research has been conducted and more is known about the role of cations in metabolism than that of the chloride ion. Some physiologists and nutritionists in the pasi have described chloride as playing a "passive role" in maintaining the body s ionic and fluid balance. With exception of the chloride shift" in venous blood, the movements of chloride have usually been considered secondary to those of the cations. 

No method in which aluminum chloride is used will give a pure product, for aluminum chloride shifts the methyl groups so that the three tetramethylbenzenes always result. These cannot be separated efficiently by any known method. 

Figure 46-9 Scheme demonstrating the isohydric and chloride shift.The encircled numbers refer to the reactions described in the text. For details, see text. 

The equilibrium between plasma and red cells has been disturbed by the reactions described so far. The concentration of HCO3 has increased relatively more in the erythrocytes than in the plasma the pH of plasma has fallen relatively more than the pH of the erythrocytes and the non-difftisible ion concentration in the erythrocytes has fallen because of the increase in protonation of proteins and hemoglobin. The membrane potential of the erythrocytes therefore becomes less negative, and the distribution of all diffusible ions must change in accordance with the new membrane potential. The ion shifts that occur rapidly are a movement of HCO3 out of the erythrocytes and a movement of Cr into the erythrocytes to provide electrochemical balance. This shift of chloride ions is referred to as the chloride shift (Figure 46-9, reactions 6 and 7). As a result of these ion fluxes, the concentration of chloride in the venous plasma is about 1 mmol/L lower than that in the arterial plasma. 

As the concentration of HCO3 (i.e., of metabolic CO2) in red blood cells increases, an imbalance occurs between the bicarbonate ion concentrations in the red blood cell and plasma. This osmotic imbalance causes a marked efflux of HC03 to plasma and consequent influx of Cl from plasma in order to maintain the balance of electrostatic charges. The latter osmotic influx, known as the chloride shift, is accompanied by migration of water to red blood cells. Thus, transport of metabolic CO2 in the blood occurs primarily in the form of plasma bicarbonate formed after CO2 diffuses into red blood cells. 

The exchange of chloride and bicarbonate across the erythrocyte membrane (the chloride shift). 

Ionization of 4-thiouracil leads to the formation of an equilibrium mixture of two monoanions in the 1 3 ratio, the N -dcprotonatcd species being predominating. The presence of calcium chloride shifts the equilibrium toward the N3-deprotonated species (74JA6832). 

Treatment of (126) with 2 equiv. of MezAlCl gives the more electrophilic aldehyde-stoichiometrically equivalent to it. This complex reacts rapidly at -78 °C to give zwitterion (129). At-78 C an irreversible [1,5] chloride shift to give chloro alkoxide (132) is the major process. At 0 C, the [1,5] chloride shift is apparently reversible, so the products obtained from (129) by three competing processes are obtained. A [1,5] methyl shift gives (130) in 30% yield, a reversible [1,5]... 

Ans. Since the cation cannot leave with the anion, the anion must exchange locations with an anion external to, and permeable to, the membrane. When the HCOj anion leaves, a Cl anion from the plasma enters the red blood cell. This is known as the chloride shift. 

The bicarbonate ions are replaced in the plasma by chloride ions that diffuse out of the blood cells. This step, called the chloride shift, maintains charge balance and osmotic pressure relationships between the plasma and red blood cells. 

The chloride shift again takes place (this time in the opposite direction) to maintain electrolyte balance. 

The propagation can also involve an intramolecular halide migration. The polymerization of 3-chloro-3-methylbutene-l proceeds at low temperatures by a chloride shift (about 50%f ... 

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