The Constitution of the Prosthetic Group of Catalase*

The constitution of the enzyme catalase is similar to that of hemoglobin. The prosthetic group is a hematin (1) and combines with a specific protein to form the enzyme molecule. Spectroscopic evidence suggests a close relationship between the porphyrin-iron complex contained in the enzyme and protohematin, the prosthetic group of hemoglobin (1). In the enzyme, however, the iron is held in the trivalent state and is unusually resistant to reducing agents (1, 2). The hematin grouping in catalase from widely different sources exhibits identical spectroscopic features (3). An apparent discrepancy in the (k/Fep) ratio (where k = catalytic activity, expressed by the monomolecular reaction constant, and (Fep) = concentration of porphyrin-bound iron) between enzyme preparations of different origins still remains to be explained. Though the dimensions of the enzyme molecule, as judged by the rate of diffusion, are probably of the same order of magnitude as those of hemoglobin (4), the protein of the enzyme complex differs from globin in the position of the isoelectric point (5) and also in its behavior towards certain precipitating agents (chloroform-alcohol). A previous synthetic approach to the problem of the constitution of the enzyme has not yielded the desired results; neither the combination of’ protohematin with simple nitrogen bases and various native and denatured proteins, nor synthetic