HAEMOGLOBIN: A PRIMORDIAL ROLE PRESERVED IN DIAPAUSE?
C.N.A. Trotman, M. Coleman, A.M. Jellie, D.C. Shieffelbien, W.P. Tate
Abstract:
Localization of immunoreactive haemoglobin in cysts of the brine shrimp Artemia by the immunogold technique showed previously that most reactivity was located throughout the cuticular layer of the cyst shell and in the embryonic exoskeleton. This hitherto unexplained finding is reassessed in the present paper against the more comprehensive profile of Artemia and other non-vertebrate globins now available. The structure of the modern Artemia globin is two polymers each containing nine globin is two polyminers each containg nine globin domains, and analysis of their sequences shows that the polymeric linkage has ancient origins in the Artemia lineage. Sequence differences between domains approach saturation, indicating a date of polymerization more than a billion years ago. Intron discordances between domains also support considerable antiquity. Seventeen intra-domain introns in each of two divergent genes have been stable in location for 60 MY, but four of these introns appear to have been displaced since the ancestral monomeric globin phase. The evident origin of haemoglobin at a time when life was microscopic and the atmosphere hypoxic or anoxic, coupled with its retention in organisms as diverse as protozoa and plant seeds, suggests a primordial role different from oxygen transport. We speculate on an origin for haemoglobin in the sequestration of oxygen released in the primordial splitting of water, a role preserved in diapause cysts to provide a reservoir of oxidative energy for the emergence mechanism.
(Department of Biochemistry, University of Otago, Box 56, Dunedin, New Zealand)