Answer:
Enzymes are usually proteins and it lowers the activation energy of a reaction. substrate binds to the active site of enzyme here the enzyme changes shapes slightly to fit tightly to the substrate, this happens at a specific temperature. Once there is an increase in temperature the enzyme denatures that is it loses shape and no longer tightly fit to the substrate.
Which in turn terminate the reaction
In other words looking at the kinetic theory of matter; Increase in temperature will increase enzymes activity. molecules will have an increase in kinetic energy hence more effective collision however since enzymes are proteins, they will rupture at elevated temperatures thereby losing their activity