The catalytic activity of enzymes depends on temperature and pH because these factors influence the enzyme's structure, stability, and interactions with substrates. Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy. They achieve this by providing an alternative reaction pathway and stabilizing the transition state. Enzymes have an optimal temperature and pH at which they exhibit maximum activity. Deviations from these optimal conditions can lead to reduced activity or even denaturation of the enzyme.1. Temperature: Enzyme activity generally increases with temperature, as higher temperatures provide more kinetic energy to the enzyme and substrate molecules, increasing the likelihood of successful collisions. However, there is an optimal temperature at which the enzyme exhibits maximum activity. Beyond this temperature, the enzyme's activity decreases due to the denaturation of its tertiary structure, which is essential for its catalytic function. Denaturation occurs when the non-covalent interactions hydrogen bonds, van der Waals forces, and hydrophobic interactions that maintain the enzyme's structure are disrupted, leading to a loss of function.Experimental evidence: In a study by Daniel et al. 1968 , the effect of temperature on the activity of the enzyme alkaline phosphatase was investigated. The enzyme activity increased with temperature up to 37C, which was the optimal temperature for the enzyme. Beyond this temperature, the enzyme activity decreased due to denaturation.2. pH: The catalytic activity of enzymes also depends on pH, as it affects the ionization state of the enzyme's active site and substrate molecules. Enzymes have an optimal pH at which they exhibit maximum activity. Deviations from this optimal pH can lead to changes in the enzyme's charge distribution, which can disrupt the enzyme-substrate interactions and reduce the enzyme's activity. In extreme cases, deviations from the optimal pH can lead to denaturation of the enzyme.Experimental evidence: In a study by Fersht 1977 , the effect of pH on the activity of the enzyme ribonuclease A was investigated. The enzyme exhibited maximum activity at a pH of 7.0. Deviations from this optimal pH led to a decrease in enzyme activity, as the ionization state of the active site and substrate molecules were altered, affecting the enzyme-substrate interactions.In conclusion, the catalytic activity of enzymes depends on temperature and pH, as these factors influence the enzyme's structure, stability, and interactions with substrates. Enzymes have an optimal temperature and pH at which they exhibit maximum activity, and deviations from these optimal conditions can lead to reduced activity or denaturation of the enzyme. Experimental evidence from studies on alkaline phosphatase and ribonuclease A supports these observations.