PH, temperature, substrate concentration in a narrow range.
Remember that enzymes work because they have specific shapes. Altering the shape alters how well they work. Changing pH and changing temperature can deform the enzyme and make it more difficult for the enzyme to work. Enzyme function can also be affected by substrate concentration, however (where substrate concentration refers to how much substrate there is in a given volume). Take for instance if there are 4 enzymes and 4 substrates. Maximum efficiency is achieved because each enzyme has a substrate to act on. If you reduce the amount of substrate to 2 substrates, theres only half efficiency. These factors act in a narrow range. What does this mean? Enzyme activity only has a narrow range of activity. Past a certain point, changing the factor wont have an effect. For instance, too high of a temperature deforms the enzyme. Past a certain temperature, the enzyme cant be deformed any more than it already is. With substrate concentration, take again the example of having 4 enzymes. Increasing the number of substrates to 5 or more wouldnt have much of an effect because there are only 4 enzymes.
