Comparative physiology and molecular evolution of carbonic anhydrase in the erythrocytes of early vertebrates.

The different isozymes of carbonic anhydrase (CA) have been the subject of intensive study in mammals, but there is still much to be learned about the early evolution of this enzyme in vertebrates. Erythrocyte CA plays an essential role in the respiratory processes of most vertebrates and is probably the most well studied CA isozyme. The available evidence indicates that there has been a progressive increase in the efficiency of erythrocyte CA during the early evolution of vertebrates. There also appears to be a substantial increase in erythrocyte CA activity during development in some species. At the present time, however, the selective pressures that may be influencing the properties of erythrocyte CA during vertebrate evolution and development have not been clearly determined. When the available molecular sequence information is examined, it is evident that the erythrocyte CAs of early vertebrates have active sites that are more similar to those of mammalian CA VII and II, rather than CA I. We can now also begin to examine the phylogenetic relationships between the different rbc CAs in vertebrates, but more CA sequence information is clearly required from different groups of vertebrates before we have a complete picture of the molecular evolution of erythrocyte CA.