phosphagen A compound found in animal tissues that provides a reserve of chemical energy in the form of high-energy phosphate bonds. The most common phosphagens are creatine phosphate, occurring in vertebrate muscle and nerves, and arginine phosphate, found in most invertebrates. During tissue activity (e.g. in muscle contraction) phosphagens give up their phosphate groups, thereby generating ATP from ADP. The phosphagens are then reformed when ATP is available.

phosphagen (fos-fă-jĕn) n. creatine phosphate (see creatine).