Multiple strategies for O2 transport:: From simplicity to complexity

O-2 carriers ( extracellular and intracellular as well as monomeric and multimeric) have evolved over the last billion of years, displaying iron and copper reactive centers; very di. fferent O-2 carriers may coexist in the same organism. Circulating O-2 carriers, faced to the external environment, are responsible for maintaining an adequate delivery of O-2 to tissues and organs almost independently of the environmental O-2 partial pressure. Then, intracellular globins facilitate O-2 transfer to mitochondria sustaining cellular respiration. Here, molecular aspects of multiple strategies evolved for O-2 transport and delivery are examined, from the simplest myoglobin to the most complex giant O-2 carriers and the red blood cell, mostly focusing on the aspects which have been mainly addressed by the so called 'Rome Group'.