<P> The biochemical identity of enzymes was still unknown in the early 1900s . Many scientists observed that enzymatic activity was associated with proteins, but others (such as Nobel laureate Richard Willstätter) argued that proteins were merely carriers for the true enzymes and that proteins per se were incapable of catalysis . In 1926, James B. Sumner showed that the enzyme urease was a pure protein and crystallized it; he did likewise for the enzyme catalase in 1937 . The conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin . These three scientists were awarded the 1946 Nobel Prize in Chemistry . </P> <P> The discovery that enzymes could be crystallized eventually allowed their structures to be solved by x-ray crystallography . This was first done for lysozyme, an enzyme found in tears, saliva and egg whites that digests the coating of some bacteria; the structure was solved by a group led by David Chilton Phillips and published in 1965 . This high - resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail . </P> <P> An enzyme's name is often derived from its substrate or the chemical reaction it catalyzes, with the word ending in - ase . Examples are lactase, alcohol dehydrogenase and DNA polymerase . Different enzymes that catalyze the same chemical reaction are called isozymes . </P> <P> The International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers; each enzyme is described by a sequence of four numbers preceded by "EC", which stands for "Enzyme Commission". The first number broadly classifies the enzyme based on its mechanism . </P>

What are some examples of enzymes in biology