In 1752, French scientist René-Antoine Ferchault de Réaumur investigated the role of gastric juices in digesting food. Later, in 1857, Louis Pasteur introduced the germ theory of fermentation, associating the process with living organisms. It was in 1893 that German chemist Wilhelm Ostwald classified enzymes as catalysts. Following this, in 1894, German chemist Emil Fischer proposed the lock-and-key model to explain how enzymes interact with their target molecules. In 1926, American chemist James Sumner obtained crystals of the enzyme urease and demonstrated that it is a protein.
A considerable amount of biochemical activity occurs in living cells as they obtain the energy required to maintain themselves. This activity, known as metabolism, involves chemical and physical changes necessary for sustaining life, including tissue repair and renewal, obtaining energy from food, and breaking down waste materials. Most of these reactions are not spontaneous; they are facilitated by catalysis, the action of catalysts. Catalysts are substances that change the rate of a reaction without themselves being altered, enabling further reactions. Enzymes, now known to be biological catalysts, facilitate the essential chemical reactions that sustain all living organisms. Without enzymes, these reactions would occur at rates too slow to sustain life.
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