Explained simply, in reversible protein phosphorylation a protein kinase takes a phosphate group from adenosine triphosphate (ATP) and attaches it to a specific site on a protein, introducing both extra mass and negative charge at that site. This can alter the protein's shape and turn its function in a biological process up or down, either by changing its activity or its ability to bind to another protein. The protein can be converted back to its original state by a protein phosphatase that removes the phosphate. This cycle controls numerous metabolic processes, and plays a central role in the regulation of cell division, shape, and motility. Derangement of specific protein phosphorylation pathways is important in human disease, including cancer and diabetes. Fischer and Krebs were awarded the Nobel Prize for Physiology or Medicine in 1992 for the discovery of reversible protein phosphorylation, .