Thank you for the opportunity to help you with your question!
composed of: a protein portion (apoenzymes) and a nonprotein portion (cofactor).
purpose: they catalyze chemical reactions by lowering the activation energy,
they are very important the life of humanity because they are help in constructing, synthesizing, carrying, dispensing, delivering, and eliminating the ingredients and chemicals used by our bodies every day.
reusable: Yes, enzymes are reusable because they are catalyst .
participates in how many different reactions: generally only participate in one type of reaction.
Activity level affected by: temparature, PH and concetration
Please let me know if you need any clarification. I'm always happy to answer your questions.