Are enzymes used up in reactions?
No, enzymes are reused.
Enzymes can be thought as catalysts for metabolic reactions. Catalysts are not used up in reactions, as they do not participate in the actual reaction, but rather provide an alternate reaction pathway with a lower activation energy.
Here is a model (lock and key model) that demonstrates the activity of an enzyme:
As you can see here, the enzyme is not used up in the reaction.