Characterization of the constituent polypeptides of the extracellular hemoglobin from Lumbricus terrestris: heterogeneity and discovery of a new linker chain L4

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The extracellular hemoglobin of Lumbricus terrestris comprises four oxygen binding chains, a, b, c, d, and three linker chains L1, L2, L3 as major components. A stoichiometry of the whole molecule has been proposed on the basis of these chains, with a total number of 216 chains: forty-eight chains of each oxygen binding chain and eight molecules of each linker chain. We have isolated additional minor components by HPLC and two-dimensional gel electrophoresis. The following biochemical characterizations have been made. (i) All components so far reported, the heme-containing chains a, b, c, d, and linker chains L1, L2, L3 and a new minor polypeptide, L4, were mapped on a two-dimensional gel. Their estimated isoelectric points were between 4.7 and 5.9. (ii) The sequences of several peptides including the unique N-terminal peptide from linker L4 show that it can be considered as a duplicated gene product with a similar mass. (iii) Chain d 2 was isolated and found to correspond to the minor chain previously pointed out by Shishikura et al. (J. Biol. Chem. 262 (1987) 3123–3131). (iv) The major chain d 1 has serine at position 7 from the N-terminus. This is not consistent with previously reported glycine (Shishikura et al., J. Biol. Chem. 262(1987)3123–3131).