Enzymes are biological catalysts. Just like other regulators, they reduce activation energy & allow reactions to proceed in a desired direction. Because the activity of the enzymes are dependent on the folding of a protein as they are usually sensitive to the temperature, pH, and salt concentration of the environment they work in. There are exceptions to this, such as the enzymes put in washing powder, but the general rule is that small deviations from their tolerable ranges can reduce activity. Larger excursions may denature them irreversibly.
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