noun Biochemistry.
any of various proteins, as pepsin, originating from living cells and capable of producing certain chemical changes in organic substances by catalytic action, as in digestion.
Compare -ase.

1880–85; < Medieval Greek énzymos leavened (Greek en- en-2 + zȳ́m(ē) leaven + -os adj. suffix)

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World English Dictionary
enzyme (ˈɛnzaɪm)
any of a group of complex proteins or conjugated proteins that are produced by living cells and act as catalysts in specific biochemical reactions
[C19: from Medieval Greek enzumos leavened, from Greek en-² + zumē leaven]

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Word Origin & History

1881, as a biochemical term, from Ger. Enzym, coined 1878 by Ger. physiologist Wilhelm Kühne (1837-1900), from Gk. enzymos "leavened," from en- "in" + zyme "leaven."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

enzyme en·zyme (ěn'zīm)
Any of numerous proteins or conjugated proteins produced by living organisms and functioning as specialized catalysts for biochemical reactions.

en'zy·mat'ic (-zə-māt'ĭk) adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
enzyme   (ěn'zīm)  Pronunciation Key 

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Any of numerous proteins produced in living cells that accelerate or catalyze the metabolic processes of an organism. Enzymes are usually very selective in the molecules that they act upon, called substrates, often reacting with only a single substrate. The substrate binds to the enzyme at a location called the active site just before the reaction catalyzed by the enzyme takes place. Enzymes can speed up chemical reactions by up to a millionfold, but only function within a narrow temperature and pH range, outside of which they can lose their structure and become denatured. Enzymes are involved in such processes as the breaking down of the large protein, starch, and fat molecules in food into smaller molecules during digestion, the joining together of nucleotides into strands of DNA, and the addition of a phosphate group to ADP to form ATP. The names of enzymes usually end in the suffix -ase.
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Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
enzyme [(en-zeyem)]

A protein molecule that helps other organic molecules enter into chemical reactions with one another but is itself unaffected by these reactions. In other words, enzymes act as catalysts for organic biochemical reactions.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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Example sentences
Most farmers feed their pigs this enzyme as a supplement.
Researchers have identified an enzyme that could hold the key to reducing
They are the product of gene splicing, turning out enzymes in quantities .
Researchers identify an enzyme crucial to healthy blood vessels, .
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