Haemoglobin oxidised

These crystals of reduced horse haemoglobin had some interesting properties which had not been observed previously. Normally when crystals of reduced haemoglobin are exposed to air they break up and most of their X-ray diffraction pattern disappears indicating that the crystals arc disordered. However when these crystals were left to become oxygenated or were slowly oxidised characteristic, well ordered lattice changes appeared. The unit cell dimensions were unchanged except for a... 

Haemoglobin (Hb) is not strictly an enzyme, since it does not catalyse directly any specific reaction. Its function is the transport of 02 from the lungs to the tissues of the mammalian body, where organic substrates are oxidised exothermically to COz and water. Hb is classified as a metalloprotein, i.e. a protein which contains and utilises atoms of low electronegativity. 

Haemoglobin is normally safely compartmentalised within the erythrocyte. It is highly susceptible to autoxidation. In the erythrocyte, there normally develops a balance between the spontaneous formation of methaemoglobin and superoxide radicals and the restoration of this oxidised haemoglobin to its normal functional state (Fig. 13 for a review see ref. [68]). 

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. 

Type II reactions are mimicked by the haemolysis induced by drugs (some antimalarials, sulpho-namides and oxidising agents) and food (broad beans) in subjects with inherited abnormahties of erythrocyte enzymes or haemoglobin (see p. 123). 

Ammonium sulphate is commonly used as a precipitant because of its great solubility and ready availability. It can liberate ammonia, which reacts with heavy atom derivatives. This problem can in some circumstances be alleviated by changing the mother liquor of the crystals to phosphate. Ammonium sulphate caused further problems in the analysis of the crystal structure of oxyhaemoglobin. In the presence of this salt and under irradiation, crystals of oxyhaemoglobin were oxidised rapidly to aqua-met-haemoglobin. The problem was solved by growing the crystals under usual conditions [34] and then transferring them to 3 M phosphate [16]. 

The solvent from which the protein was crystallised can alter the properties. In the presence of ammonium sulphate, oxyhaemoglobin is oxidised rapidly to aquamet-haemoglobin on irradiation. This problem has been overcome by a change to phosphate salts [16], as discussed previously. 

Fe-enriched cytochrome c from Torula utilis yeast strain 321 has been similarly examined at low temperatures, and the S = i oxidised form is basically similar to haemoglobin cyanide [22]. Spectrum simulation using the e.s.r. g-values for horse-heart cytochrome c was partially successful. The applied-field technique gave a positive value for e qQ in the S = 0 iron(II) cytochrome c, with an asymmetry parameter of rj 0-5,... 

The reactions of haemoglobin derivatives in their oxidised (Fe ") form with ligands have also been studied kinetically. The reactions tend to be... 

As ordinarily prepared, haematin is a mixture of a ferric porphyran, methcem, and a ferrous porphyran, hwm. Haemoglobin, itself, is a chromoprotein formed by the union of globin and haem, and when oxidised to oxyhaemoglobin, the haem component is converted into a labile form, oxy-haem. Drastic oxidisers change the ferrous oxy-haem into the ferric methaem, as occurs when methaemoglobin is prepared. 

A primary goal in management is to remove cyanide from cytochrome oxidase so aerobic metabolism can resume. Since cyanide has a higher affinity for ferric iron, sodium nitrite is administered to oxidise haemoglobin (Fe " to methaemoglobin... 

Sodium nitrite oxidises the iron component of haemoglobin, resulting in formation of methaemoglobin which cyanide binds to preferentially over cytochrome oxidase. This allows resumption of cytochrome oxidase activity and the subsequent restoration of aerobic cellular metabolism. 

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