To test that, we have examined the pH dependence of RHR and OHR in the range of 7.5-10.0. The kinetic curves were fitted with a double exponential model yielding two eigenvalues λ1 and λ2 (Figure ). For the RHR, the λ1 was in the range of 100 to 130 s -1 with a slight optimum at pH 9.0, while λ2 was in the range of 0-20 s -1 and was linearly decreasing from pH 7.5 to 10.0. In the OHR reaction with DCPIP, the observed eigenvalues were much lower than those observed for RHR and the highest λ1 was observed at 7.5, indicating the pH optimum at lower pH values, which were unfortunately beyond the experimentally accessible range due to the rapid aggregation of the enzyme.