Comparison of the catalytic and physical properties of the components of lyophilized beef erythrocyte catalase with those of lyophilized beef liver catalase components

Abstract

The catalytic and physical properties of the components of lyophilized beef erythrocyte catalase have been studied, and compared to those of lyophilized beef liver catalase which were reported by us previously (10). The molecular weight of Component I, which sediments much more slowly than native catalase, is 81,000–82,000 in the case of beef erythrocyte and liver catalase subjected to lyophilization. Component II, the only other component found by us in lyophilized erythrocyte catalase, has a molecular weight of 217,000–244,000, which is close to that of native erythrocyte catalase. Comonent I and Component II have been separated on the basis of their solubility in 0.1 M phosphate buffer-15% NaCl. Spectral analysis of dithionite-treated Component II shows that 60–70% of this whole molecule fraction is nonreducible catalase, while enzyme assay shows that this fraction has a Kat. f. of 10–20% that of native catalase. Component I, which has one-third the molecular weight of native erythrocyte catalase, usually is completely reducible by dithionite and has a molar extinction coefficient at 405 mμ which is one-quarter that of native catalase and Component II. The ratio of the extinction coefficients at 405 mμ of native beef erythrocyte catalase and Components I and II of lyophilized erythrocyte catalase to the extinction coefficients at 405 mμ of the corresponding liver catalase preparations is in all cases close to 1.5. This value reflects the greater hematin content of the erythroeyte enzyme. It is concluded from the above results that during the lyophilization of beef erythrocyte and beef liver catalases, some of the enzyme is dissociated into third molecules, while a portion of the remainder is modified in conformation, leading to its becoming reducible by dithionite. The catalytic activity of lyophilized erythrocyte catalase varied from one-sixth to one-twenty-third of the activity of the native enzyme. The catalytic activity of Component II in most cases was greater than that of Component I and varied from one-fifth to one-tenth of the native enzyme. The catalytic activity of Component I obtained from beef erythrocyte catalase lyophilized as an aqueous suspension of crystalline plates or as a buffered solution was so low as to be considered zero as was the case with Component I obtained from beef liver catalase lyophilized as an aqueous suspension of crystalline plates, prisms, or as a buffered solution. Beef erythrocyte catalase third molecules obtained through the lyophilization of an aqueous suspension of erythrocyte catalase prisms possess variable but possibly significant catalytic activity, which can be as high as one-fourteenth of that found in the native enzyme. It is proposed that the presence of catalytic activity in the erythrocyte catalase third molecules may be due to the increased hematin content in the erythrocyte subunit as compared to the liver subunit. Possible implications of the above findings to a hypothetical model of the catalytic action of catalase involving coordinated action of two or more hematins are discussed.