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Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals) which catalyzes the decomposition of hydrogen peroxide to water and oxygen. [5] It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS).
During the day, CAM plants close stomata and use stored acids as carbon sources for sugar, etc. production. The C3 pathway requires 18 ATP and 12 NADPH for the synthesis of one molecule of glucose (3 ATP + 2 NADPH per CO 2 fixed) while the C4 pathway requires 30 ATP and 12 NADPH (C3 + 2 ATP per CO 2 fixed).
Several costs are associated with this metabolic pathway; the production of hydrogen peroxide in the peroxisome (associated with the conversion of glycolate to glyoxylate). Hydrogen peroxide is a dangerously strong oxidant which must be immediately split into water and oxygen by the enzyme catalase.
In plants, both enzymes can catalyze the oxidation of ortho-diphenols substrates into their corresponding ortho-quinones. The key difference between the two related enzymes is that tyrosinase can catalyze the hydroxylation of monophenols to diphenols (monophenolase activity) as well as the oxidation of the o-diphenol to the o-quinone ...
Some plants have evolved mechanisms to increase the CO 2 concentration in the leaves under these conditions. [ 30 ] Plants that use the C 4 carbon fixation process chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP ...
Additionally, enzymes including superoxide dismutase, catalase, and peroxidase contribute to the oxidation response by reducing the presence of hydrogen peroxide, which is a prevalent precursor of the hydroxyl radical (OH•).
Respiratory burst requires a 10 to 20 fold increase in oxygen consumption through NADPH oxidase (NOX2 in humans) activity. NADPH is the key substrate of NOX2, and bears reducing power . Glycogen breakdown is vital to produce NADPH.
An increase in catalytic speed may be favoured as it could confer some advantage to the organism. However, when the catalytic speed outstrips diffusion speed (i.e. substrates entering and leaving the active site, and also encountering substrates) there is no more advantage to increase the speed even further.