Enzymes act as biocatalysts that speed up nearly all biochemical reactions, yet in the late 19th century they were viewed as a special “vital force” that existed only inside living cells. Sumner purified urease from jack beans using alcohol precipitation and repeated recrystallization, and in 1937 showed with X-ray diffraction that it formed an ordered crystalline lattice. The result proved that enzymes are proteins and can be handled with ordinary physico-chemical techniques in a test tube. This breakthrough laid the groundwork not only for enzymology but also for modern biotechnology and pharmaceutical manufacturing. Detergent proteases and the enzymes used in blood-glucose test strips, for instance, would not exist without the ability to prepare pure enzymes. Sumner’s work is celebrated as a key step that erased the boundary between life and chemistry.

To demonstrate that enzymes are macromolecular proteins, Sumner extracted jack-bean meal with dilute acid, followed by acetone/ethanol precipitation, dialysis, and pH-controlled isoelectric precipitation to obtain crystals of urease that retained catalytic activity. He measured optical rotation and total nitrogen content of the crystals, confirming the absence of non-protein cofactors and concluding that urease is a single protein species. His methodology strongly influenced later separations of large enzyme complexes and spurred the evolution of chromatographic techniques. Crystallization of enzymes opened the door to X-ray crystallography for determining their three-dimensional structures, effectively inaugurating structural biology. Access to pure samples allowed rigorous testing of enzyme kinetics such as the Michaelis–Menten equation, thereby establishing quantitative enzymology. The cascade of techniques derived from this work underpins today’s large-scale production of industrial enzymes, biosensors, and enzyme engineering, forming a cornerstone of the modern bioindustry.

Sumner precipitated crude urease extract with 70 % ethanol and recrystallized the fraction appearing near pH 4.8, yielding single-protein crystals with >90 % purity. Specific optical rotation [α]D = -66° combined with Karl Fischer titration refined the protein content and ruled out cofactors or glycan moieties. Low-angle X-ray scattering in 1937 revealed a hexagonal unit cell (a = 134 Å) consistent with a ~480 kDa homohexamer. Activity assays in the crystal phase showed that the Ni2+ catalytic center remained intact, providing an early example of reversible metalloprotein crystallization. These data bridged colloid chemistry and emerging molecular biology, technologically underpinning subsequent hemoglobin structure determinations.