Oxygenation, haemoglobins

Alternatively, if this agent is not available, the cyanide can be made to bind to the haemoglobin in the patient s blood, which will bind cyanide if it is in a particular (known as oxidised) form. Some of the patient s haemoglobin can be converted to the oxidised form by giving him/her a substance called nitrite. The cyanide in the blood then binds to the oxidised haemoglobin. Oxygen can also be given with these treatments and seems to help. 

In the concerted model, the first binding of substrate increases the affinity of the other active sites, but further bindings have no effect. This doesn t contradict the haemoglobin/oxygen binding constants presented earlier, as the increased affinities at ever increasing oxygen concentrations could be due to the increased proportion of relaxed form, rather than to individual increases in each protein molecule (Fig. 6.16). 

Fig. 6.2. Haemoglobin-oxygen binding curve. Note the increase in sigmoidicity as the Hill coeflicient (h) increases from I to 5.

In the complex, haemoglobin, oxygen or carbon monoxide can displace one of the imidazole groups there is a consequent redistribution of electrons (bringing 12 electrons to the ferrous ion) with formation of... 

Wang T, Branco LGS, Glass ML. Ventilatory respnses to hypoxia in the toad, Bufo paracnemis, before and after a decrease in haemoglobin oxygen-carrying capacity. J Exp Biol 1994 196 1-8. 

Hill (1913) proposed, for the haemoglobin-oxygen system, an equation which accounts for the sigmoid nature of the curve and which can be written, when applied to enzyme phenomena, in the form... 

One of the most important reactions of dioxygen is that with the protein haemoglobin which forms the basis of oxygen transport in blood (p. 1099). Other coordination... 

Table 12. Parameters of reversible oxygen transport for haemoglobin and a microdisperse form of immobilized haemoglobin (pH 7.4, 37 °C, pC02 = 40 Torr, p02 = 0-150 Torr)...

Bettati S et al Allosteric mechanism of haemoglobin Rupture of salt-bridges raises the oxygen affinity of the T-structure. J Mol Biol 1998 281 581. 

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