ABSTRACT
In contrast with the hemoglobins of the vertebrates, which are almost invariably intracellular and tetrameric, the intra- and extracellular hemoglobins of the invertebrates show a wide variety in their molecular size and architecture. The expression of the individual hemoglobins of Artemia and their oxygen binding characteristics are regulated in such a way that the animal is able to cope with extreme differences in environmental conditions. The structure of the Artemia globins is not an exception but rather an example of a vast group of invertebrate extracellular hemoglobins containing high molecular size globin chains. Each globin chain binds eight heme groups, or one heme per domain molecular size 17,000, which is in accordance with the minimum molecular weight calculated from amino acid composition. The invertebrate extracellular hemoglobins can be classified into four groups. They are: single-domain, single-subunit hemoglobins; single-domain, multisubunit hemoglobins; two-domain, multisubunit hemoglobins; and multidomain, multisubunit hemoglobins.
