Catalytic kinetics and activation energy of soil peroxidases across ecosystems of differing lignin chemistries
| Autor: | Nishanth Tharayil, Caroline M. Preston, Daniella J. Triebwasser-Freese, Patrick Gerard |
|---|---|
| Rok vydání: | 2015 |
| Předmět: |
biology
Chemistry fungi technology industry and agriculture complex mixtures Michaelis–Menten kinetics chemistry.chemical_compound mental disorders Soil water Botany biology.protein Environmental Chemistry Lignin Terrestrial ecosystem Composition (visual arts) Ecosystem Monolignol Earth-Surface Processes Water Science and Technology Peroxidase |
| Zdroj: | Biogeochemistry. 124:113-129 |
| ISSN: | 1573-515X 0168-2563 |
| Popis: | Factors regulating the persistence of lignin in terrestrial ecosystems are highly debated, and recently lignin has been proposed to have a low residence time in soils. The catalytic efficiency and activation energy of the oxidoreductase enzymes regulate the residence time of lignin in soils. We characterized the spatial and seasonal changes in the apparent Michaelis–Menten kinetics and activation energy of soil peroxidases in three ecosystems of differing litter chemistries- pine forest, deciduous forest, and agricultural ecosystem. Peroxidases rarely follow true Michaelis–Menten kinetics, hence we measured the apparent K m ( App K m ) and apparent V max ( App V max ) of soil peroxidases under potentially H2O2 non-limiting conditions using 3,3′,5,5′-tetramethylbenzidine as the reducing substrate. The App V max and App K m measured in this study, when used independently, exhibited only a weak relationship with total quantity and composition of lignins. Hence, we adopted the ratio of these two parameters ( App V max / App K m ) to define the apparent catalytic efficiency ( App CE) of peroxidases. Across the three ecosystems and seasons, the App CE of peroxidase was ecosystem specific, and exhibited a strong correlation with the monolignol composition of the resident plant species. The App CE of peroxidase was higher in agricultural soils that had lower lignin content. Pine soils with a higher relative proportion of vanillyl units that contribute to more recalcitrant inter-unit linkages in lignins exhibited the highest App V max and App K m , resulting in the lowest App CE. This decoupling of App CE of peroxidases from chemistry of the native lignin observed in our assay-system could indicate a relatively longer persistence of lignin in ecosystems receiving recalcitrant litter inputs. Even though the apparent activation energy ( App Ea) of peroxidases varied by depth and seasons across ecosystems, the App Ea did not relate to the chemistry or quantity of lignins, probably due to the substrate-saturated assay conditions. Our study captures the apparent kinetics of peroxidases in soils, which was ecosystem specific, and in part regulated by the composition of monolignols, thus providing a preliminary linkage between lignin chemistry and enzyme properties in natural systems. |
| Databáze: | OpenAIRE |
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