METAL-CATALYZED OXIDATION OF FE2- CONSENSUS TARGET SEQUENCE BETWEEN PROPANEDIOL OXIDOREDUCTASE OF ESCHERICHIA-COLI AND ALCOHOL-DEHYDROGENASE-II OF ZYMOMONAS-MOBILIS( DEHYDROGENASES )

We have studied two enzymes of a newly described family of dehydrogena ses with high sequence homology, 1,2-propanediol oxidoreductase of Esc herichia coli and alcohol dehydrogenase II of Zymomonas mobilis. These enzymes perform their metabolic role under anaerobic conditions; in t he presence of oxygen, they show a very similar inactivation pattern b y a metal-catalyzed oxidation system. Titration of histidine residues with diethyl pyrocarbonate showed one histidine residue less in the ox idized enzymes. Comparison of subtilisin peptide maps of active and in activated enzymes showed a difference in one histidine-containing pept ide, the sequence of which is YNTPH(277)GVAN for propanediol oxidoredu ctase and YNLPH(277)GV for alcohol dehydrogenase II. This histidine re sidue lies 10 residues away from a proposed metal-binding site, H(263) XXXH(267), necessary to explain a site-specific free radical mechanism . The three histidine residues here described are strictly conserved i n all enzymes of this family. In this report we propose that histidine 277 is a target for oxidation by a metal-catalyzed oxidation system a nd that this modification leads to the irreversible inactivation of bo th enzymes.