Linker Chains of the Gigantic Hemoglobin of the Earthworm Lumbricus terrestris: Primary Structures of Linkers L2, L3, and L4 and Analysis of the Connectivity of

ABSTRACT The extracellular hemoglobin (Hb) of the earthworm, Lumbricus terrestris, has four major kinds of globin chains:a, b, c, andd, present in equimolar proportions, and additional non-heme, non-globin scaffolding chains called linkers that are required for the calcium-dependent assembly of the full-sized molecule. The amino acid sequences of all four of the globin chains and one of the linkers (L1) have previously been determined. The amino acid sequences via cDNA of each of the three remaining linkers, L2, L3, andL4, have been determined so that the sequences of all constituent polypeptides of the hemoglobin are nowknown. Each linker has ahighly conserved cysteine-rich segment of 40 residues that is homologous with the seven ligand-bindin