Active site structure of the catalase-peroxidases from Mycobacterium tuberculosis and Escherichia coli by extended X-ray absorption fine structure analysis

The catalase-peroxidase encoded by katG of Mycobacterium tuberculosis is a more effective activator of the antibiotic isoniazid than is the equivalent enzyme from Escherichia coil. The environment of the heme iron was investi gated using X-ray absorption spectroscopy to determine if differences in th is region were associated with the differences in reactivity. The variation in the distal side Fe-ligand distances between the two enzymes was the sam e within experimental error indicating that it was not the heme iron enviro nment that produced the differences in reactivity. Analysis of variants of the E. coil catalase-peroxidase containing changes in active site residues Arg102 and His106 revealed small differences in Fe-water ligand distance in cluding a shorter distance for the His106Tyr variant. The Arg102Leu variant was 5-coordinate, but His106Cys and Arg102Cys variants showed no changes w ithin experimental error. These results are compared with those reported fo r other peroxidases. (C) 2001 Elsevier Science B.V. All rights reserved.