PMID: 39622Jun 19, 1979

Differential effects of pH and inositol hexaphosphate on the spectroscopic properties of the alpha and beta subunits in methemoglobins M Milwaukee and A

Biochimica Et Biophysica Acta
M E John, M R Waterman


The effect of pH and inositol hexaphosphate on the electron spin resonance spectra of the alpha-hemes (g = 6.0) and the beta-hemes (g = 6.7) has been measured in methemoglobin M Milwaukee and compared with that of methemoglobin A (g = 6.0). The beta-hemes are found to be comparatively insensitive to both effectors while the alpha-hemes behave in a manner similar to the heme groups of methemoglobin A. Binding of inositol hexaphosphate enhances the high spin ESR signal of the alpha-hemes in both methemoglobins. Comparison of the optical properties of methemoglobins A and M Milwaukee over the pH range from 5.0 to 8.1 shows that inositol hexaphosphate has a differential effect on the subunit types in these two methemoglobins. At low pH the spectral changes observed upon inositol hexaphosphate binding arise primarily from the beta-hemes, while at neutral and alkaline pH these changes arise from both subunit types. The beta-heme spectral changes appear to be pH independent while those arising from the alpha-hemes are strongly pH dependent. It is concluded that it is the hydroxymet form of the alpha-hemes which undergoes spectral change upon inositol hexaphosphate binding to the beta-subunits. In methemoglobin A the spin state and par...Continue Reading


Mar 16, 1981·European Journal of Biochemistry·M E John, M R Waterman

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