Question

What is the effect of excess heat or temperature on an enzyme

Answer 1

Enzymes are proteins and if have an optimal working condition each one is different this if for both Temp and Ph the best way to picture it is like frying an egg when the egg comes out its all runny as soon as it gets to hot the egg solidifies and you can never make it runny again same thing with an enzyme 

Answer 2

An enzyme is a protein, and proteins need certain temperatures to function optimally, or even function. Temperature may unfold the protein and may stop its functioning, or it may fold the protein into the correct formation to function. But by the way your question asks, EXCESS heat would denature the enzyme and cease function.