Hemoglobin temperature effect

We studied the effects of total and partial deuteration on the kinetics of thermal denaturation of met-hemoglobin. The kinetics were shown to be first order with respect to protein concentration this was true both in H2O and in D2O within the entire range of temperatures examined. Deuterium oxide increased the stability of the native conformation of met-hemoglobin this effect increased progressively by increasing the amount of D2O in the solution. Extension of the experiments to the amplest possible temperature range (50-63°C) allowed the determination of the isotopic effect on the activation enthalpy and entropy of the denaturation reaction the isotopic effect resulted to be mainly entropic. 

The concept of equilibrium is also important in biochemical processes such as O2/CO2 exchange in hemoglobin (for example, see exercise 5.8 at the end of this chapter), the binding of small molecules to DNA strands (as might occur in the transcription process), and the interaction of substrates and enzymes. Temperature effects are important in protein denaturation process. Clearly, the ideas established in this chapter are widely applicable to all chemical reactions, even very complex ones. 

This theory clearly predicts that the shape of the polymer length distribution curve determines the shape of the time course of depolymerization. For example Kristofferson et al. (1980) were able to show that apparent first-order depolymerization kinetics arise from length distributions which are nearly exponential. It should also be noted that the above theory helps one to gain a better feeling for the time course of cytoskeleton or mitotic apparatus disassembly upon cooling cells to temperatures which destabilize microtubules and effect unidirectional depolymerization. Likewise, the linear depolymerization kinetic model could be applied to the disassembly of bacterial flagella, muscle and nonmuscle F-actin, tobacco mosaic virus, hemoglobin S fibers, and other linear polymers to elucidate important rate parameters and to test the sufficiency of the end-wise depolymerization assumption in such cases. 

Of greatest interest are those compounds that attempt to model hemoglobin directly. Simple iron(II) porphyrins are readily autoxidized first to superoxo species, then to //-peroxo dimers and finally to /x-oxo dimers, as represented in equation (60). Bridge formation must be prevented if carrier properties are to be observed. This has been achieved by the use of low temperature and sterically hindered or immobilized iron(II) porphyrins. Irreversible oxidation is also hindered by the use of hydrophobic environments. In addition, model porphyrins should be five-coordinate to allow the ready binding of 02 this requires that one side should be protected with a hydrophobic structure. Attempts have also been made to investigate the cooperative effect by studying models in which different degrees of strain have been introduced. 

Temperature independent electron tunneling was observed also in Ref. [319], where the rate of electron transfer over large distance in mixed-metal hemoglobin hybrids [MP, FeIU(CN )P], where M = Zn or Mg, was measured in the temperature range from ambient to 100 K. The electron transfer from the triplet state of MP to Fera was not effected by the freezing of the cryosolvent, which may indicate that coupling of electron transfer to low-frequency solvent modes may be minimal. For both M, but especially for M = Mg, the rate constant of the back reaction is nearly temperature independent. 

Kinoshita K., Chatzipanteli K., Alonso O. F., Howard M., and Dietrich W. D. (2002) The effect of brain temperature on hemoglobin extravasation after traumatic brain injury. J. Neurosurg. 97,945-953. 

The dependences, such as Eq. 2.47, are known as compensation effect, and coefficient (3C is denoted as isokinetic temperature at which all reactions of given series have the same rate constant. An example of compensation effect for for catalytic rate constant of the Sulfolobus solfataricus p-glycosidase reaction with different substrates is shown in Fig. 2.19. Similar relationships were reported for many other prosesses, involving the binding ligands to hemoglobin, the oxidation of alcohols by catalase, the hydroxylation of substrates by cytochrome c, etc. 

L. H. Laasberg and J. Hedley-Whyte. Halothane solubility in blood and solutions of plasma proteins effects of temperature, protein composition, and hemoglobin concentration. Anesthesiology, 32, 351-6(1970)... 

Benesch RE, Benesch R, Yu CL The oxygenation of hemoglobin in the presence of 2,3-diphosphoglycer-ate. Effect of temperature, pH, ionic strength, and hemoglobin concentration. Biochemistry 1969 8 2567-71. 

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