wife of Switzerland so they chose to settle there. Reversible protein phosphorylation Six months after his arrival in Seattle, Fischer learnt of fellow biochemist from the same university, Edwin G. Krebs, who was also trying to answer a similar question on where muscles received the energy that they needed to contract. Fischer began collaborating with Krebs, and the duo began their investigations on glycogen phosphorylase, an enzyme that had been discovered by the husband and wife pair of Gerty Cori and Carl Ferdinand Cori who had won the Nobel Prize for the discovery in 1947. Krebs had earlier studied the enzyme in the muscle tissue, while Fischer had studied the enzyme in a potato. The duo realized a discrepancy in that the enzyme in the muscle required an additional chemical to function, while the potato did not require that additional chemical. Krebs and Fischer defined a series of reactions leading to the activation/inactivation of this enzyme as triggered by hormones and calcium, and in the process discovering reversible protein phosphorylation. They had discovered that the muscle enzyme was regulated by the addition and removal of phosphate groups in a process called reversible phosphorylation. Explained simply, reversible protein phosphorylation works like this: a protein kinase moves a phosphate group from adenosine triphosphate (ATP) to a protein, converting it to adenosine diphosphate (ADP). The shape and the function of this protein is thus altered enabling it to take part in converting glycogen into glucose which is used for fuel for muscular contractions. When the protein has completed its role a different protein phosphatase removes the phosphate and the protein reverts to its original state. This cycle takes place to control an enormous number of metabolic processes. While the importance of the discovery was not fully recognised in 1955, the discovery became core to explaining one of the fundamental mechanisms that cells use to communicate with one another. Phosphorylation determines how a cell grows, divides, differentiates and eventually dies. The reaction also regulates hormones and proliferation of cancerous cells. The regulation of phosphorylation was determined to be key to understanding diseases such as cancer, diabetes, and heart disease. Many modern drugs build on the work done by Fischer and Krebs including attempting to manipulate the process. For the discovery of reversible protein phosphorylation, Fischer and Krebs were awarded the Nobel Prize for Physiology or Medicine in 1992, for explaining how the reaction acted