Enzyme

An enzyme is a biological molecule, almost always a protein, that speeds up a specific chemical reaction inside a living cell without being consumed by it. The physiologist Wilhelm Kuhne coined the term in 1877, from the Greek for "in yeast," to name the fermenting agents in yeast whose nature was then unknown. Louis Pasteur held that fermentation could occur only inside a living cell, but Eduard Buchner's 1897 discovery that a cell-free yeast extract could ferment sugar on its own, and Emil Fischer's 1894 lock and key model proposing that an enzyme and its target molecule fit together like a key and its lock, together established that an enzyme is a definite chemical substance whose action follows from its own structure rather than from the life of the cell that made it.