A re-evaluation of the molecular mass of earthworm extracellular hemoglobin from meniscus depletion sedimentation equilibrium. Nature of the 10 S dissociation species

Previous calculations from meniscus depletion sedimentation equilibrium of the molecular mass of earthworm hemoglobin from Lumbricus terrestris (E.J. Wood et al., Biochem. J. 153 (1976) 589-596) and from the related species Lumbricus sp. (L. sp.) (M.M. David and E. Daniel, J. Mol. Biol. 87 (1974) 89-101) were made on the assumption that the solutions behaved ideally. Re-examination of their results reveals, however, a dependence of the apparent molecular mass on concentration. Taking this effect into consideration, we have now recalculated from their data molecular masses of 4.4-4.5 MDa for the hemoglobin of both L. terrestris and L. sp. On the basis of the new determinations, we propose for the polypeptide chain composition of L. terrestris hemoglobin a model [(abcd)₄L1L2L3]₁₂ where a,b,c,d are the four globin and L1,L2,L3 are the three major linker chain constituents of the protein. The model is consistent with the D₆ symmetry of the molecule. A 10 S intermediate product in the alkaline dissociation of Lumbricus hemoglobin is viewed as a binary mixture of products resulting from a disproportionation reaction involving the structural unit. The present interpretation is shown to be consistent with observed relations between molecular masses and SDS gel electrophoretic band patterns of 10 S species and intact hemoglobin. Copyright (C) 1999 Elsevier Science B.V.