The molecules that act as energy storage molecules in muscle by donating a phosphorus to resynthesize ATP and ADP are called phosphocreatine and creatine. Phosphocreatine is a high-energy phosphate compound that is found in skeletal muscle and other tissues. When the muscle needs energy, phosphocreatine can rapidly donate a phosphate to ADP to form ATP, which can then be used for muscle contraction. Creatine is the precursor to phosphocreatine and can be synthesized in the liver and kidneys from amino acids.