The enzyme-substrate compounds of bacterial catalase and peroxides

Abstract

Bacterial catalase formed primary and secondary enzyme-substrate complexes with H2O2, methyl-H2O2 and ethyl-H2O2. The spectra of the bacterial and erythrocyte catalase-methyl-H2O2 complexes in the region of the Soret band were nearly identical. However, a quantitative difference existed between the Soret bands of the primary H2O2 complex of bacterial and erythrocyte catalases. The velocity constant (at 20-25[degree]) for the decomposition of H2O2 in the presence of bacterial catalase was 5.3 x 107M-1sec.-1 for a four-hematin catalase, and might be compared with the value of 3.5 x 107 for erythrocyte catalases; i.e., the ratio of the velocity constants (or of the Kat. f. values) for the 2 enzymes is 1.5:1. The velocity constant for the combination of bacterial catalase with H2O2 was about 6 x 107 [image]-1sec.-1. The velocity constants for the combination of bacterial catalase with methyl- or ethyl-H2O2 were 2.2 x 105 and 2.8 x 103 [image] -1sec-1, respectively. These values were about 10 times slower than the corresponding values for erythrocyte catalases. The primary bacterial catalase-peroxide complexes reacted with acceptors according to the mechanisms found to obtain for the corresponding erythrocyte catalase-peroxide complexes; only the green primary complexes appeared to be involved in these reactions. The specificity appeared to follow an identical pattern; velocity constants were evaluated for nitrite, formaldehyde, formate, methanol, ethanol and propanol. In the reactions of bacterial catalase with substrates or acceptors, the values of the reaction velocity constants were dependent on the size of the substrate or acceptor molecule to a much greater extent than was found to be the case with erythrocyte catalase; large molecules reacted much more slowly than small ones. This greater dependence was interpreted to indicate that the hematins of bacterial catalase were "buried" in the protein molecule to a greater extent than were the hematins of erythrocyte catalase. Nevertheless, the hematins of bacterial catalase reacted with H2O2 more rapidly than did the hematins of erythrocyte calatase. It was suggested that the proximity of the protein groups to the hematins of bacterial catalase enhanced their activity towards molecules to which the hematins were accessible.