Magnetic Susceptibility and EPR Measurements of Catalase and Its Derviatives

The molar paramagnetic susceptibilities (moie) per Fe3+ ion of free catalase [EC 1.11. 1.6] and its fluoride, cyanide and azide compounds were measured with a magnetic torsion balance over the range from room temperature to liquid nitrogen temperature. From the slopes of the linear relationships for Kmoie-1T, the values of the effective Bohr magneton number (nerr) were found to be 5.96 for free catalase, 5.78 for the fluoride compound and 2.63 for the cyanide compound. However, the curve for Zmoi1T of the azide compound deviated markedly from Curie's law. This can be explained by assuming that there is a thermal equilibrium between the high-spin (S=5/2) and low-spin (5=1/2) states of the hematin irons of this compound. From the data that the proportion of the low-spin form to the total concentration of the hematin irons of this compound increased on lowering the temperature, the energy level of the low-spin state seems to be lower than that of the high-spin state. The EPR spectrum of the azide compound was measured at 20°K and 77°K. The spectrum at 20°Kappeared to be more of low-spin type than at 77°K. This tendency accords with the results obtained from the magnetic susceptibility measurements.