Phosphagens are a group of molecules that includes creatine phosphate (in vertebrates), and arginine phosphate, lombricine, and phosphoopheline (in invertebrates). These molecules have similar functions in different organisms. The structure of creatine phosphate is H O C (double bond O) C H 2 N (C H 3) C (N H 2) N P O 3 2 minus. The structure of lombricine phosphate is P O 3 2 minus N H C (N H) N H C H 2 C H 2 P O 4 minus C H 2 C H (N H 2) C (double bond O) O H. The structure of arginine phosphate is P O 3 2 minus N H C (N H) N H C H 2 C H 2 C H 2 C H (N H 3 plus) C (double bond O) O H. The structure of phosphoopheline is C H 3 P O 4 minus C H 2 N H C (N H) N H P O 3 2 minus. What functions do these molecules have in common? They can be chemically converted to ATP, which is hydrolyzed to ADP to provide energy. They can accept phosphoryl groups from ATP when ATP is present in excess. They can donate phosphoryl groups to ADP to regenerate ATP. They can take the place of ATP in metabolic reactions when [ATP] is low in the body. They increase the strength and size of muscle tissue.