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How did Eduard Buchner show that yeast enzymes could work outside living cells?
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Enzyme
In the induced-fit theory of enzyme-substrate binding, a substrate approaches the surface of an enzyme (step 1 in box A, B, C) and causes a change in the enzyme shape that results in the correct alignment of the catalytic groups (triangles A and B; circles C and D represent substrate-binding groups on the enzyme that are essential for catalytic activity). The catalytic groups react with the substrate to form products (step 2). The products then separate from the enzyme, freeing it to repeat the sequence (step 3). Boxes D and E represent examples of molecules that are too large or too small for proper catalytic alignment. Boxes F and G demonstrate binding of an inhibitor molecule (I and I′) to an allosteric site, thereby preventing interaction of the enzyme with the substrate. Box H illustrates binding of an allosteric activator (X), a nonsubstrate molecule capable of reacting with the enzyme.
Eduard Buchner demonstrated that fermentation could occur outside of living cells by using a cell-free extract known as press juice.1
In 1897, Buchner showed that this yeast press juice, which was devoid of living yeast cells, still contained an enzyme he called zymase. This extract was capable of breaking down sugar into alcohol and carbon dioxide. By successfully reducing a complex biological process to a nonliving system of enzymes, Buchner provided evidence that fermentation is a chemical process resulting from the action of enzymes rather than the activity of the yeast cell itself. This discovery was a significant milestone in biochemistry, earning him the 1907 Nobel Prize for Chemistry.21