Factors Affecting Rates of Enzyme Catalyzed Reactions

Factors Affecting Rates of Enzyme Catalyzed Reactions      Enzymes can only affect the rate at which a reaction occurs. Factors that affect the rate of reactions include: 1. Catalytic Rate    Catalytic rate is a property of the enzyme itself. Strictly speaking it is a measure of how fast the enzyme can produce product per unit time if the active site is always occupied by a substrate molecule. 2. Enzyme Concentration    The more enzyme molecules there are the more product molecules can be generated per unit time. 3. Substrate Concentration    The higher the substrate concentration the higher the reaction rate. At higher substrate concentration the active site is occupied a higher percentage of time.    Percent saturation indicates the proportion of time that the active site is occupied. As the substrate concentration increases the percent saturation increases. As the proportion of occupied active site increases, at some point the enzyme active sites are 100% occupied and the saturation is 100%. At 100% saturation only increasing the catalytic rate of the enzyme and/or the concentration of the enzyme will increase the catalytic rate.    An enzyme with a high affinity for substrate has a higher percent saturation at an particular substrate concentration. 4. Affinity    This is a measure of how tightly the substrate molecule binds to the active site. Higher affinities usually mean higher rates. Affinity is influenced by how well substrate molecules fit on an active site and by the existence of any attraction between the substrate molecule and the active site such as opposite electrical charges. Additional Factors Other factors that influence enzyme activity include temperature and pH. However, within living cells these two factors are held within normal limits.