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Tracing the Impact of a Unique Loop in Catalase‐peroxidase Catalysis
Author(s) -
Kudalkar Shalley Nidhish,
Goodwin Douglas C
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.715.11
Subject(s) - peroxidase , catalase , chemistry , heme , active site , cytochrome c peroxidase , hydrogen peroxide , enzyme , biochemistry , tyrosine , stereochemistry
Catalase‐peroxidases (KatGs) catalyze hydrogen peroxide decomposition by two distinct mechanisms using a single active site. This active site catalyzes substantial catalase turnover even though it bears no resemblance to classical catalases. Instead, the active site is superimposable on classical peroxidases like cytochrome c peroxidases, enzymes which have little if any catalase activity. One of the unique features imparting this bifunctionality is large loop 1 (LL1). LL1 forms part of a substrate access channel to heme buried in the active site and provides the tyrosine residue in the unique methionine‐tyrosine‐tryptophan covalent adduct essential for catalase but not peroxidase activity. This study focuses on identifying additional roles of LL1 in the unique catalytic properties of KatGs. Variants lacking portions of LL1 were subjected to steady state and transient state kinetic analysis. All variants showed a complete loss of catalase activity but the deletion variants showed substantial increase in peroxidase activity compared to wild type and Y226F enzyme. This increase in peroxidase activity was traceable to rapid reduction of high oxidation state intermediates by exogenous electron donors, and coincident prevention of enzyme inactivation by peroxides. These results highlight the role of LL1 as a gate keeper to limit typical peroxidase activity in favor of catalase turnover. Y226F has no catalase activity and insufficient capability to use exogenous electron donors to sustain peroxidase activity. This project was supported by National Science Foundation (MCB‐ 0641614).