Typical Catalases: Function and Structure

Catalase (EC 1.11.1.6) is a heme-containing enzyme ubiquitously present in most aerobic organisms. Although the full range of biological functions of catalase still remains unclear, its main function is the decomposition of hydrogen peroxide into water and oxygen. Catalases have been studied for over 100 years, with examples of the enzyme isolated, purified, and characterized from many different organisms. The crystal structures of 16 heme-containing catalases have now been solved, revealing a common, highly conserved core in all enzymes. The active center consists of a heme with a tyrosine ligand on the proximal side and a conserved histidine and an aspartate on the distal side. Although catalases have been studied for many years, additional functions of catalases have recently been recognized. For example, Scytalidium thermophilum catalase (CATPO) has been shown to oxidize o-diphenolic and some p-diphenolic compounds in the absence of hydrogen peroxide. This and other studies have led to the proposal that this secondary oxidative activity may be a general characteristic of catalases. The present chapter will focus on the function and structure of monofunctional heme catalases, emphasizing the information obtained in the last few years mainly in relation to the secondary activity of these enzymes

Role of Active Site Residues on Catalytic Activity of Catalase with Oxidase Activity from Scytalidium Thermophilum

AbstractScytalidium thermophilum produces a catalase with phenol oxidase activity (CATPO) that catalyses the dismutation of hydrogen peroxide (H2O2) 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

Developmental and biochemical analyses of in vitro drought stress response in ornamental European Bluestar (Amsonia orientalis Decne.)

This study aimed to investigate the effects of drought stress on Amsonia orientalis, an endangered ornamental plant with a limited natural distribution in Europe. Effects of polyethylene glycol (PEG)-mediated drought stress (-0.15, -0.49, -1.03 and -1.76 MPa osmotic potentials) were tested on in vitro cultures. In general, root lengths and numbers, total protein, chlorophyll a and carotenoid contents were negatively influenced at elevated levels of the stress factor. The successive decrease in the tested osmotic potentials resulted in gradually higher H2O2, malondialdehyde (MDA) and proline contents. Activities of the antioxidant enzymes, peroxidase (POD) and catalase (CAT), were found to be enhanced in response to the decreasing osmotic potential tested, whereas increased superoxide dismutase (SOD) activity was observed at the -0.15 MPa osmotic potential. Strong activation of POD enzymes under drought stress suggests that POD enzymes might have a major role in regulating the H2O2 content, while CAT has only a supplementary role in A. orientalis. These results indicated that although A. orientalis is susceptible to long-term drought, the species may survive during mild drought stress because the development of the plant was not totally inhibited but only limited. Nevertheless, the species should be introduced to well-irrigated lands, after evaluation of the soil’s water status, in order to ensure the continuation of its generations

Production of a novel bifunctional catalase-phenol oxidase of Scytalidium thermophilum in the presence of phenolic compounds

A novel bifunctional catalase with additional phenol oxidase activity (CATPO) is produced by the thermophilic fungus, Scytalidium thermophilum, in a growth-associated manner. In order to study the biological significance of this dual enzyme in relation to phenolic compounds, 14 phenolics were tested for their effect on growth and CATPO production. It was determined that some phenolics exerted a negative effect on growth (catechol, coumaric acid, hydroquinone, kaempferol, myricetin), while others either did not influence growth in a negative manner or enhanced growth by a maximum of 50% increase in biomass (caffeic acid, chlorogenic acid, catechin, gallic acid, resorcinol, vanillic acid). Hydroquinone and myricetin showed an antifungal effect and enhanced CATPO production, while catechol, coumaric acid, and kaempferol decreased CATPO production and showed a toxic effect at higher doses. In general, phenolics acting in an antioxidant manner exhibited a reverse interrelation with CATPO production. These results suggest that the presence of antioxidant phenolic compounds has an effect on enhancing its antioxidant activity; enzyme is therefore no longer required