Major Events in the Evolution of the Oxygen Carriers

Abstract

SYNOPSIS. Major events in the history of the blood O2 carriers in multicellular animals include: 1) The origin of the red blood cell hemoglobins, which are both the most primitive and the most advanced O2 carriers. At the molecular level, they are believed to have arisen only once; at the animal level, there is no cogent reason to postulate more than two origins. 2) The origin of the hemerythrins, which occur at about the same phylogenetic level as the primitive red blood cell hemoglobins. They may not have been selected in higher animals because of their temperature sensitivity. The origins of 3) the molluscan hemocyanins and 4) the arthropod hemocyanins. These two events occurred independently, though for similar reasons. Both kinds of hemocyanins offered physiological advantages over the primitive hemoglobins that were important in the context of the more advanced molluscan and arthropod cardiovascular systems. 5) The origins of extracellular heme proteins, which arose independently many tunes, and probably for as many different reasons. 6) The loss of urea sensitivity, and the acquisition of organic Po4 sensitivity and additional cooperativity and pH dependence by the red blood cell hemoglobins, which occurred well after the origin of the vertebrates.