Bonds guanidine phosphate

The most important type of acid anhydride in biochemistry is that between two molecules of phosphoric acid, as exemplified by the two terminal bonds of ATP (p. 67), but the pyrophosphate bond is not the only type of energy-rich bond as can be seen from Table XI. Mixed anhydrides of carboxylic and phosphoric acids (acyl-phosphates), phosphorylated enol groups (enolphosphates), phosphorylated guanidine groups (guanidine phosphates), compounds of sulphhydryl groups with phosphoric or carboxylic acids (thioesters or thiophosphates), all these types of compound are energy-rich. 

---