On the synthesis and degradation of the multiple forms of catalase in mouse liver

The incorporation of ⁵⁵Fe-labeled ferrous sulfate and ³H-labeled γ-aminolaevulinic acid into the catalase of mouse liver was measured at intervals up to 96 hr after intraperitoneal injection, and the intracellular location of radioactive catalase followed, as well as the distribution of radiolabel between the multiple forms of this enzyme. At 10 min, catalase radioactivity was present in all the cellular fractions studied, but after this time, label began to disappear from the microsomal fraction and from the peroxisomal detergent extract. By comparison, catalase incorporation reached a peak at about 6 hr in the peroxisomal aqueous extract, and rose to a broad peak after about 30 hr in the cytosol fraction. On resolving the multiple forms of catalase in the supernatant fraction by electrophoresis, it was found that label first appeared in the fastest moving heteromorph, and appeared sequentially in the other multiple forms over a period of 96 hr.The sequence of degradation of catalase was also studied by examination of residual catalase activity subsequent to the injection of allyl-isopropyl acetamide, a heme synthesis antagonist which blocks catalase synthesis. Blood catalase levels did not seem to be significantly affected by this treatment, but in the liver, the decay rates of catalase activity were appreciable, and varied significantly between the intracellular pools. The rate of decrease was greatest in the peroxisomal detergent extract, and least in the supernatant fraction.These findings have been discussed in relation to current understanding of the subcellular disposition, multiplicity, and turnover of hepatic catalase.