John Northrop shared the Nobel Prize in chemistry in 1946 with Wendell Stanley, awarded to them "for their preparation of enzymes and virus proteins in a pure form," and with James Sumner, "for his discovery that enzymes can be crystallized." Although Sumner had been the first, in 1926, to crystallize an enzyme (urease) and to aver that enzymes were proteins, Northrop did more than any other scientist to establish that pure enzymes are indeed proteins.
About 1920 Northrop repeated the earlier claim of Cornelis Pekelharing that he had isolated a protein from gastric juice (the enzyme pepsin). Neither Pekelharing nor Northrop was able to crystallize the protein. However, Sumner's crystallization of urease encouraged Northrop to take up the problem again. In 1930 Northrop isolated a crystalline substance from a commercial pepsin preparation, and the crystallized substance appeared to be the enzyme pepsin. Subsequently Northrop, together with Moses Kunitz, isolated and crystallized trypsin, trypsinogen, chymotrypsin, and chymotrypsinogen.
Northrop carefully tested his enzyme preparations by means of solubility measurements, ultracentrifuge analysis, and electrophoresis , and concluded that they were essentially pure proteins. From measurements of diffusion, denaturation, hydrolysis, and the formation of active enzyme from inactive precursor, he concluded that enzymatic activity was a property of the protein molecule itself and was not due to a nonprotein impurity.
Northrop had long had an interest in viruses and bacteriophage—things that occupied his attention increasingly in his later years. Though he was more concerned with the protein component of bacteriophage than their nucleic acid component, in 1951 he made the prophetic suggestion: "The nucleic acid may be the essential autocatalytic self-reproducing part of the molecule, and the protein portion may be necessary only to allow the entrance to the host cell."
John Howard Northrop was born into an academic family in Yonkers, New York, in 1891. He entered Columbia University in 1908, from which institution he received his Ph.D. in chemistry in 1915. In 1916 he was appointed to the Rockefeller Institute, and he remained there for the rest of his working life. In 1924 he transferred to the Princeton branch of the institute, where most of his significant work on proteins was performed. In 1949, when the institute closed its Princeton branch, Northrop moved to the University of California at Berkeley as professor of bacteriology and biophysics, while remaining a member of the institute and continuing to receive its support for his work. He retired in 1959. He died in 1987, aged ninety-five.
Herriott, R. M. (1983). "John H. Northrop: The Nature of Enzymes and Bacterio-phage." Trends in Biochemical Sciences. 13:296–297.
Robbins, F. C. (1991). "John Howard Northrop (5 July, 1891–May 27, 1987)." Proceedings of the American Philosophical Society 135:315–320.
Northrop, John. Nobel lecture. Available from http://www.nobel.se/chemistry/laureates .