engleski

PROTON MAGNETIC-RELAXATION STUDY OF INTERACTION BETWEEN METHEMOGLOBIN AND INOSITOL HEXAPHOSPHATE

Inositol hexaphosphate is the strongest allosteric effector even for the metform of haemoglobin. Its effects upon the quaternary structure of the tetramer have been studied in relation to the overall conformational state(s) of the haem-pockets in aqueous solutions of human haemoglobins. The method used, proton magnetic relaxation, yields information about the accessibility of solvent protons towards the haem-iron. No differences in the relaxation rates were detected by this method between the unstripped carbonmonoxyhaemoglobin and the phosphate-stripped sample in the presence and absence of IHP. There are considerable changes in those relaxation rates due to the paramagnetic haem-iron of aquomethaemoglobin when IHP is added to the stripped adult haemoglobin, but none is observed for the foetal haemoglobin, although a similar shift in the spin-state equilibrium is expected for both haemoglobins on addition of IHP. Neither was there any change with IHP in solutions of adult fluoromethaemoglobin. It is concluded that there is no tightening of haem-pockets upon addition of IHP to the solution of any of the three haemoglobin samples. An increase in accessibility of the haem-pocket is probable only for the aquometform of the adult haemoglobin. It is suggested that the structural aspect of ligand affinity, i.e. the haem-pocket conformation, is not as decesive in altering the affinity by IHP as is possibly the change in the haem-iron spin-state induced by IHP-binding.

Haemoglobin ; Inositol hexaphosphate ; Proton magnetic relaxation ; stereochemical probe

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