The importance of arginine in evolution.

The special chemistry and metabolism of arginine has been considered in relation to the evolution of metabolic and structural features of animals. Arginine and compounds derived from it act in muscle as a major reserve of ATP and as a regulatory sink for phosphate. The metabolism of arginine in less complex animals has been extended to produce urea, firstly as an osmotic regulator and subsequently as a means for terrestrial animals to excrete surplus nitrogen. The ornithine component of arginine is metabolised to form important polyamines and also proline. It is also argued that the change from phosphoarginine to phosphocreatine was a permissive step in the development of the vertebrates which are rich in connective tissue.