Haemoglobins

Haemoglobin.— The kinetics of the binding of CO to human methaemoglobin, in which only one haem group is reduced by eaq to the ferrohaem form, have been measured in unbuffered solution at pH 6.2  

Reaction (41) was followed by monitoring changes in the concentrations of [HbFez +Fe +] and [HbFe3 +Fe +CO], and both observations gave (4.1 0.2) X 10 s under conditions where the dimer-tetramer equilibrium 

The alternative explanation of the effect of IHP on binding rates in terms of a shift in the dimer-tetramer equilibrium (see above) was discounted on the grounds that the reaction kinetics were independent of protein concentration (10—40 //M based on tetramer). In contrast to the data of ref. 53, the kinetics of CO binding in the presence of IPH were biphasic at pH 6.8, and it is suggested that IHP induces different reactivity in the a- and jS-chains towards CO. 

Both organic radicals are 100% efficient in reducing the iron centre, indicating direct interaction with the haem group, whereas only about 40% of the OH reaction leads to reduction. A likely reason for this is that -OH forms a radical on the protein that can undergo other reactions as well as transfer an electron to the haem group. 

The superoxide ion Og shows no reaction with oxyhaemoglobin and reacts very slowly ( = 1.4 x 10 s ), if at all, with methaemoglobin. The reaction 

Probe Properties of the Spin-States and their Equilibrium A. Introduction and Haemoglobin 

We have shown in the previous sections that the spin-equilibrium is very finely balanced in the Fe(III) form of several proteins and their derivatives. The exact position of balance is sensitive to temperature, pH 

A similar change in spin-state balance of the aquo form of haemoglobin Fe(III) can be seen on change of pH or even of ionic strength. 

It could be said that we have not offered proof of the postulate that the iron-histidine distance is altered. In one sense this is not true for we have found that the Mossbauer spectrum of the iron(III) is altered by pH and ionic strength changes. This is a probe of the iron nucleus. However it would be better to have a probe of the nitrogen or the hydrogens of the imidazole. This is now available through the refinement of NMR techniques. Other possibilities are the use of cobalt(II) porphyrin as a probe to examine the Co(II)—N (histidine) distance through EPR super-hyperfine structure studies, and the use of Mn(III) porphyrin for the 

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There has been extensive work done on myoglobin, haemoglobin, Cytocln-ome-c, rhodopsin and bacteriorhodopsin. In fact, there are literally hundreds of articles on each of the above subjects. Flere we will consider haemoglobin [12]. The first tliree of these examples are based on the protohaeme unit, shown in figure Bl.2.10. 

Figure Bl.2.10. Structure of the protohaeme unit found in haemoglobin and myoglobin.

Wliat are the structural dynamics of the tetramer as a whole The haemoglobin bound to O2 (Flb02) is not photoactive, so the CO adduct, FlbCO, is used instead. 

Figure Bl.2.11. Biologically active centre in myoglobin or one of the subunits of haemoglobin. The bound CO molecule as well as the proximal and distal histidines are shown m addition to the protohaeme unit. From Rousseau D L and Friedman J M 1988 Biological Applications of Raman Spectroscopy vol 3, ed T G Spiro (New York Wiley). Reprinted by pennission of John Wiley and Sons Inc.

Scott T W and Friedman J M 1984 Tertiary-structure relaxation in haemoglobin—a transient Raman-study J. Am. Chem. Soc. 106 5677-87... 

Figure C2.5.1. The 3D native stmcture of haemoglobin visualized using RasMol 2.6 [8], The linear sequence of amino acids of haemoglobin is given below tire figure.

Wlien a strong electron-donor ligand such as pyridine is added to tlie reaction mixture, it can bond so strongly to tlie Rli tliat it essentially drains off all tlie Rli and shuts down tlie cycle it is called a catalyst poison. A poison for many catalysts is CO it works as a physiological poison in essentially the same way as it works as a catalyst poison it bonds to tlie iron sites of haemoglobin in competition witli O. ... 

Dasgupta S, Copeland R A and Spiro T G 1986 Ultraviolet Raman spectroscopy indicates fast ( 7 ns) R->T-like motion in haemoglobin J. Biol. Chem. 261 10 960-2... 

Hofrichter J, Sommer J H, Henry E R and Eaton W A 1983 Nanosecond absorption spectroscopy of haemoglobin Proc. Natl Acad. Scl. USA 80 2235-9... 

Figure C3.1.7. Time-resolved optical absorjDtion data for the Soret band of photo lysed haemoglobin-CO showing six first-order (or pseudo-first-order) relaxation phases, I-VI, on a logaritlimic time scale extending from nanoseconds to seconds. Relaxations correspond to geminate and diffusive CO rebinding and to intramolecular relaxations of tertiary and quaternary protein stmcture. (From Goldbeck R A, Paquette S J, Bjorling S C and Kliger D S 1996 Biochemistry 35 8628-39.)...

Carbon monoxide, CO. Carbon monoxide is a colourless, odourless gas. It is extremely poisonous, since the haemoglobin of the blood... 

Perhaps the most important complex of iron(II) is heme (or haeme). Haemoglobin, the iron-containing constituent of the blood, consists essentially of a protein, globin, attached through a nitrogen atom at one coordination position of an octahedral complex of iron(II). Of the other five coordination positions, four (in a plane) are occupied by nitrogen atoms, each of which is part of an organic... 

Absorption spectra of standard solutions of Cyt c was obtained at different concentration. Maximum of absolution was observed at wavelength 410 nm. It is known haemoglobin and other haems have absolution maximum at the same wavelength. For elaboration of selective method of Cyt c determination in semm of mice its reaction with phtalocyanine of copper was investigated. Absorption maximum of Cyt c with Cu phtalocyanine in H SO was observed at wavelength 710 nm. Dependence on optical density at 710 nm against concentration of Cyt c have linear character in range 0.162-10-"-6.49-10 mol/L. 

Haemoglobin A (from normal human blood) [9008-02-0] -64,500, amorphous. 

Perutz, M.F. New x-ray evidence on the configuration of polypeptide chains. Polypeptide chains in poly-g-benzyl-t-glutamate, keratin and haemoglobin. Nature 167 1053-1054, 1951. 

Perutz, M.F., et al. Structure of haemoglobin. A three-dimensional Fourier synthesis at 5.5 A resolution, obtained by x-ray analysis. Nature 185 416-422, 1960. 

Fermi, G., et al. The crystal stmcture of human deoxy-haemoglobin at 1.74 A resolution. /. Mol. Biol. 

Fermi, G., Pemtz, M.F. Atlas of Molecular Structures in Biology. 2. Haemoglobin and Myoglobin. Oxford,... 

Ingram, V.M. Gene mutation in human haemoglobin the chemical difference between normal and sickle cell haemoglobin. Nature 180 326-328, 1957. 

CARBON MONOXIDE Carboxyhaemoglobin in blood End of shift 3.5% of haemoglobin B, Ns... 

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