Two globin strains in the giant annelid extracellular haemoglobins

The constituent polypeptide chains I, II, III and IV of the giant extracellular haemoglobin of the oligochaete Lumbricus terrestris were isolated by mono Q ion-exchange chromatography and C8 reverse-phase chromatography. The N-terminal amino acid sequences of Lumbricus chains I, III and IV were determined and aligned with those of Lumbricus chain II and the four chains of the extracellular haemoglobin of the polychaete Tylorrhynchus heterochaetus. Three invariant amino acid residues, Cys-7, Val-15 and Trp-19, were found to occur in the N-terminal segments (17-22 residues) of the eight chains of Lumbricus and Tylorrhynchus haemoglobins. In addition, it was found that the eight sequences could be separated into two groups: 'A', consisting of Lumbricus chains I and II and Tylorrhynchus chains I and IIA, having invariant Lys-14 and Lys-16, and 'B', consisting of Lumbricus chains III and IV and Tylorrhynchus IIB and IIC, having invariant Cys-6, Ser-8 and Asp-11. This result suggests that there are two strains of globin chain in the annelid extracellular haemoglobins.