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Why were the crystallization of urease and pepsin important to enzyme research?

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A multi-panel diagram illustrates how a substrate binds to an enzyme's active site through induced fit, leading to product formation, and shows how non-substrates and allosteric regulators can alter enzyme activity by binding to different sites on the enzyme. — 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.

The crystallization of urease by James B. Sumner in 1926 and pepsin by John Howard Northrop in 1930 were landmark achievements in biochemistry that fundamentally transformed the scientific understanding of enzymes.123

Prior to these breakthroughs, the chemical nature of enzymes was a subject of significant debate and uncertainty. By successfully isolating and crystallizing these enzymes, Sumner and Northrop provided the necessary evidence to resolve this dispute, demonstrating that enzymes are proteins.214

These achievements were critical for several reasons:
* Identification of Chemical Nature: The ability to obtain enzymes in a pure, crystalline form allowed researchers to prove that they are composed of amino acid chains, establishing them as proteins rather than some other unknown substance.234
* Foundation for Enzymology: This work laid the essential groundwork for the field of enzymology, enabling further studies into enzyme structure, function, and the specific chemical reactions they catalyze within living systems.124
* Recognition: Both scientists were awarded the Nobel Prize for Chemistry in 1946 for their pioneering contributions to the purification and crystallization of enzymes.123