Multiple strategies for O2 transport: From simplicity to complexity

O2 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 different O2 carriers may co-exist in the same organism. Circulating O2 carriers, faced to the external environment, are responsible for maintaining an adequate delivery of O2 to tissues and organs almost independently of the environmental O2 partial pressure. Then, intracellular globins facilitate O2 transfer to mitochondria sustaining cellular respiration. Here, molecular aspects of multiple strategies evolved for O2 transport and delivery are examined, from the simplest myoglobin to the most complex giant O2 carriers and the red blood cell, mostly focusing on the aspects which have been mainly addressed by the so called 'Rome Group'.