Explained simply reversible protein phosphorylation works like this: a protein kinase moves a phosphate group from adenosine triphosphate (ATP) to a protein. The shape and the function of the protein is 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.