Comparative study of catalase-peroxidases (KatGs)

Catalase-peroxidases or KatGs from seven different organisms, including Archaeoglobus fulgidus,Bacillus stearothermophilus, Burkholderia pseudomallei, Escherichia coli, Mycobacterium tuberculosis, Rhodobacter capsulatus and Synechocystis PCC 6803, have been characterized to provide a comparative picture of their respective properties. Collectively, the enzymes exhibit similar turnover rates with the catalase and peroxidase reactions varying between 4900 and 15,900 s−1 and 8–25 s−1, respectively. The seven enzymes also exhibited similar pH optima for the peroxidase (4.25–5.0) and catalase reactions (5.75), and high sensitivity to azide and cyanide with IC50 values of 0.2–20 μM and 50–170 μM, respectively. The KMs of the enzymes for H2O2 in the catalase reaction were relatively invariant between 3 and 5 mM at pH 7.0, but increased to values ranging from 20 to 225 mM at pH 5, consistent with protonation of the distal histidine (pKa approximately 6.2) interfering with H2O2 binding to Cpd I. The catalatic kcat was 2- to 3-fold higher at pH 5 compared to pH 7, consistent with the uptake of a proton being involved in the reduction of Cpd I. The turnover rates for the INH lyase and isonicotinoyl-NAD synthase reactions, responsible for the activation of isoniazid as an anti-tubercular drug, were also similar across the seven enzymes, but considerably slower, at 0.5 and 0.002 s−1, respectively. Only the NADH oxidase reaction varied more widely between 10−4 and 10−2 s−1 with the fastest rate being exhibited by the enzyme from B. pseudomallei.