The structure of Scytalidium thermophilum catalase in complex with its well known inhibitor 3-amino-1,2,4-triazole revealed that the inhibitor occupies a surface pocket at the end of the lateral channel. This pocket corresponds to the site of NADPH binding in mammalian catalases. Peroxide-independent phenolic substrate oxidation is likely to occur in a similar manner to NADPH oxidation.
Scytalidium thermophilum produces a catalase with phenol oxidase activity (CATPO) that catalyses the dismutation of hydrogen peroxide (H 2 O 2 ) to dioxygen and water and also oxidizes several phenolic compounds in the absence of hydrogen peroxide. It comprises 717 amino acids with a 19 amino acid signal sequence, and a 17 amino acid prosequence. It is a homotetrameric protein of molecular mass 320 kDa and subunit molecular mass 80 kDa. Although catalases have been studied for many years, a peroxide independent oxidative activity of catalases has recently been recognized. There are a great number of reports available describing the structural and biochemical characterization of catalases. However basic questions related to substrate and product flow remain unanswered, particularly related to the oxidase activity. The goals of our current studies are to investigate the main and lateral channels known that connect the deeply buried active site to the exterior of the enzyme. We have introduced a number of mutations into these regions and analyzed their specific activities.
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