John Howard Northrop (1891-1987) was awarded a quarter of the 1946 Nobel Prize in Chemistry for purifying enzymes and virus proteins. In 1929, he isolated and crystallized the gastric enzyme pepsin and determined that it was a protein. He later isolated and crystallized pepsinogen, trypsin, chymotrypsin, and carboxypeptidase. Northrop also studied the proteins of viruses and antibodies and succeeded in isolating a nucleoprotein which had bacteriophage activity. He suggested that this activity was due to nucleic acid, which was later proven to be correct. His later research included work on the origin of viruses and their relationship with the “transforming principle,” which was invoked to explain how bacteria transfer genetic information and is now known to be DNA.