Temperature: rate of enzyme activity increases as temperature increases, more kinetic energy, molecules move faster, higher frequency of successful collisions. If temperature is above the optimum, the tertiary structure is altered, so the active site is altered, and the reaction stops as the substrate is no longer complementary.
pH: enzymes have an optimum pH at which they work best; alteration means denaturation of the enzyme and substrate, making the active site no longer complementary.
Concentration of enzyme: more enzyme molecules increase the likelihood of substrate collisions and the formation of enzyme-substrate complexes. If the substrate is limited, there is no more reaction since the enzyme no longer has substrate available.
Concentration of substrate: more substrate leads to more successful collisions, up to the saturation point where all active sites are taken up