The Nobel Prize-winning American biological chemist John Howard Northrop (1891-1987) established that enzymes are proteins and also showed that a bacterial virus is a nucleic acid-protein complex.
On July 5, 1891, J. H. Northrop was born in Yonkers, NY. He attended Columbia University, majoring in chemistry and earning a bachelor of science degree in 1912 and a masters degree in science in 1913. He studied the nature of phosphorus in starch for his thesis research and received a doctoral degree in chemistry in 1915. Northrop accepted a position with the biologist Jacques Loeb at the Rockefeller Institute for Medical Research in New York City.
In his early career, Northrop was concerned with the effect of environmental factors on the hereditary properties of fruit flies (Drosophila). He began by growing the flies aseptically, without pathological microorganisms. It was probably the first time animals had been cultivated free of microorganisms. Northrop found that although carbon dioxide output, a measure of energy expended, was greater at 15°C than at 22°C, the flies lived longer at 15°C than at 22°C. This discovery exploded the existing hypothesis that life duration was regulated by an energy limit.
The entrance of the United States into World War I cut short Northrop's fruit fly research. His talents were needed by the Federal government to produce acetone for the war effort. He was commissioned a captain in the Army's chemical warfare service. In a short time Northrup developed a method of fermentation of potatoes which produced substantial quantities of acetone.
After the war Northrop returned to the Rockefeller Institute and began studying enzymes. He first tried to determine the conditions which affect the action of the digestive enzymes pepsin and trypsin. By 1929 he had obtained crystals of swine pepsin, but it was not until 1931 that his failure of any of his methods to separate the enzymatic activity from the proteinous material finally convinced him that pepsin must be protein—another significant discovery.
Throughout his career Northrop had an interest in self-duplicating systems, one of the prime characteristics of living units. This interest led him to examine, in the 1920s, the way in which tobacco mosaic virus and bacterial viruses (bacteriophages) reproduce. These studies prepared him for work in the late 1930s in which he showed that highly purified staphylococcus bacteriophages contained nucleic acid as well as protein. This was one of the earliest demonstrations of the presence of nucleic acid in virus. Later he drew attention to the possibility that the nucleic acid in bacterial viruses might correspond to the free deoxyribonucleic acid (DNA) of the transforming principle, which in the virus is encased in a protein unit that serves to protect the DNA and to introduce it into the susceptible cell.
Northrop became a full member of the Rockefeller Institute for Medical Research (now Rockefeller University) in 1923, after Loeb's death. He retained that position throughout his life. He was elected to membership in the National Academy of Sciences in 1934. He shared the Nobel Prize in chemistry in 1946 with his Rockefeller colleague Wendell F. Stanley and with Cornell University's James B. Summer for their work on purification and crystallization of enzymes.
After the closing of the Rockefeller Laboratories in Princeton, New Jersey, Northrop moved to Berkeley, California. There he became a professor of bacteriology and biophysics at the University of California at Berkeley, and he continued to work on mechanisms by which viruses arise in apparently healthy cells. He served as a contributing editor of the Journal of General Physiology, beginning in 1925.
Northrop died at his home in Wickenberg, Arizona, on May 27, 1987, after a long retirement. His son-in-law, Frederick Robbins, was also a Nobel Prize recipient, capturing the 1954 award in physiology and medicine.
Most of Northrop's research papers were published in the Journal of General Physiology; he also wrote a book, Crystalline Enzymes (1939; rev. ed. 1948); The Nobel Foundation's Chemistry (3 vols., 1964-1966) contains a biography of Northrop; Information on Northrop and his work is also found in Eduard Farber, ed., Nobel Prize Winners in Chemistry, 1901-1950 (1953); and in Paula McGuire, ed., Nobel Prize Winners (1992).