Multiple strategies for O2 transport: from simplicity to complexity

O2carriers (extracellular and intracellular as well as monomeric and multimeric) have evolved over the last billion of years, displaying iron and copper reactive centers; very different O2carriers may co‐exist in the same organism. Circulating O2carriers, faced to the external environment, are responsible for maintaining an adequate delivery of O2to tissues and organs almost independently of the environmental O2partial pressure. Then, intracellular globins facilitate O2transfer to mitochondria sustaining cellular respiration. Here, molecular aspects of multiple strategies evolved for O2transport and delivery are examined, from the simplest myoglobin to the most complex giant O2carriers and the red blood cell, mostly focusing on the aspects which have been mainly addressed by the so called 'Rome Group'.