Dissociation of catalase. A correlation between changes in sedimentation and spectroscopic properties accompanying dissociation of bacterial catalase in alkaline solution

[摘要]

1. At high concentrations, in 10mm-phosphate buffer, pH7.0, the sedimentation coefficient of bacterial catalase varies with concentration according to: [Formula: see text] with S⁰_20,w=11.30S and k_s=6.29×10⁻³ml mg⁻¹. Sedimentation-equilibrium experiments yield a molecular weight of 240000. 2. Parallel studies of changes in sedimentation-velocity behaviour and in electronic spectra of bacterial catalase at pH>11 were made. Dissociation is indicated by the appearance of a slow-moving (2.9S) component in sedimentation patterns and this is accompanied by marked changes in absorption spectrum in the Soret region. Values of R=E₄₀₆/E₃₅₅ show a theoretically predictable near-linear dependence on α, the degree of dissociation calculated from ultracentrifuge data. 3. The Soret absorption of bacterial catalase subunits is much lower than that of the native enzyme, and it is suggested that dissociation produces an environmental constraint on the prosthetic group that results in distortion of the porphyrin ring.