• A protein that speeds up chemical reactions in the body.
  NCI Dictionary of Cancer Terms
  U.S. National Cancer Institute, 2021
• A substance that speeds up another chemical reaction. For example, digestive enzymes help speed up the digestion of food.
  Harvard Dictionary of Health Terms
  Harvard Medical Publishing, 2011
• Molecules that catalyze a chemical reaction. They are usually proteins, although catalytic RNA and DNA molecules have been identified.
  NCI Thesaurus
  U.S. National Cancer Institute, 2021
• Protein molecules that possess catalytic activity; they may occur naturally or be synthetically created; for catalytic RNA use RIBOZYME.
  CRISP Thesaurus
  National Institutes of Health, 2006
• Biological molecules that possess catalytic activity. They may occur naturally or be synthetically created. Enzymes are usually proteins, however CATALYTIC RNA and CATALYTIC DNA molecules have also been identified.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2021
• Enzyme, a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process. A brief treatment of enzymes follows. For full treatment, see protein: Enzymes. The biological processes that occur within all living...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2020