The haem-accessibility to solvent and allosteric effects in different protomers of human haemoglobins as observed by proton magnetic relaxation

1. 1. The temperature dependence of the paramagnetically induced molar solvent-proton longitudinal magnetic relaxation (PMR) rates in the phosphate-free solutions of aquomet derivatives of human haemoglobins A₀ and A₂ are almost identical. 2. 2. The addition of inositol hexaphosphate to either of the solutions increases the PMR rates, but this effect is significantly smaller for HbA₂. 3. 3. Taking into account the non-equivalent influence of α and β chains on PMR rates, it is concluded that the mechanism of transfer of the allosteric information upon binding of inositol hexaphosphate is less effective in HbA₂ than in HbA₀. Some implications of this finding are discussed here.