The son of a physician, Hans Krebs attended several German universities before receiving his medical degree from the University of Hamburg in 1925. Although he set up practice as an ear, nose and throat specialist (his father's occupation), he soon realized he preferred doing research and, a year later, became an assistant to the noted biochemist Otto Warburg at the Kaiser Wilhelm Institute in Berlin, Germany. While there, Krebs became interested in amino acids, the building blocks of protein. He particularly wanted to know more about the then-unknown process by which the body, under certain circumstances, breaks down the amino acids instead of using them for constructive purposes.

In the course of several years of research, Krebs discovered that when amino acids were broken down (or degraded), their nitrogen atoms were the first to be stripped away. After this deamination process, the nitrogen atoms were excreted from the body...