John Howard Northrop, an American biochemist, shared the 1946 Nobel Prize in chemistry with 2 other biochemists, James B. Sumner (1887-1955) and Wendell M. Stanley (1904-1971), for successfully purifying and crystallizing certain enzymes, thus allowing the chemical nature of these substances to be determined. Stanley crystallized and studied the tobacco mosaic virus, Sumner isolated and crystallized a protein he considered to be urease, and Northrop isolated and identified several enzymes. Northrop was born on July 5, 1891, in Yonkers, NY. His father was a zoology instructor at Columbia University in New York City, and his mother was a botanist. Just before Northrop was born, his father was killed in a laboratory explosion, and his mother had to resume her position as a botany teacher at HunterCollege in New York City. Northrop attended elementary and secondary schools in New York and graduated from high school in 1908. After graduation, he entered Columbia University and received a BA degree in 1912, an MA degree in 1913, and a PhD degree with a major in chemistry in 1915. After receiving his doctorate, Northrop was awarded a 1-year traveling fellowship that allowed him to work at the Rockefeller Institute for Medical Research (New York City). Subsequently, he was appointed an assistant at the institute, and in 1917, he became an associate to the faculty. During World War I (1914-1918), Northrop served as a captain in the US Chemical Warfare Service and conducted research on fermentation processes suitable for the industrial production of acetone and ethyl alcohol. After the war, he returned to the Rockefeller Institute and resumed his investigations on protein. This work led to the study of enzymes. In 1920, enzymes were relatively mysterious substances, although they had been discovered in 1902 by German chemist Eduard Buchner (1860-1912), who won the Nobel Prize in chemistry in 1907. Northrop's research on enzymes led to the crystallization of pepsin in 1930. In the course of this work, he established that pepsin is a protein, thus resolving the dispute about whether enzymes were proteins. Using the same chemical methods, he also helped to isolate and prepare in crystalline form the inactive precursor of pepsin pepsinogen (which is converted to the active enzyme through a reaction with hydrochloric acid in the stomach), the pancreatic digestive enzymes trypsin (1932) and chy-motrypsin (1935), and their inactive precursors trypsinogen and chymotrypsinogen. In 1938, he isolated the bacterial virus (bacteriophage) and proved that the virus was anucle-oprotein. From 1916 to his retirement in 1961, Northrop was associated with the Rockefeller Institute for Medical Research in New York City. During World War II (1939-1945), he served as a consultant and official investigator for the National Defense Research Committee. His wartime work led to the development of methods for the automatic detection of chemical weapons. From 1949 to 1958, he also served as a visiting professor of bacteriology and biophysics at the University of California at Berkeley and was resident biophysicist at the Donner Laboratory there from 1958 to 1959. Among his many scientific literary efforts was his 1939 book Crystalline Enzymes. On May 27, 1987, at the age of 95 years, Northrop died in Wickenburg, Ariz (about 45 miles northwest of Phoenix). He was honored on a stamp issued by Gabon in 1995.