Towards a resolution of the long-standing controversy regarding the molecular mass of extracellular erythrocruorin of the earthworm Lumbricus terrestris

Ezra Daniel, Ariel Lustig, Melvyn M. David, Yossi Tsfadia

Research output: Contribution to journalArticlepeer-review

Abstract

The published molecular mass of erythrocruorin of Lumbricus terrestris and related earthworm species covers a bewildering range of 3.23-4.5 MDa. A critical reexamination reveals that some mass determinations were underestimated and the results do cluster, not at one, but at two values of the molecular mass. One cluster corresponds to ∼3.6 MDa, as predicted for a stoichiometry of 144 globin and 36 linker chains - the Vinogradov model for the hexagonal bilayer (HBL) assembly of Lumbricus erythrocruorin - and as estimated from the crystal structure of HBL at 5.5 Å resolution [Proc. Natl. Acad. Sci. U. S. A. 97 (2000) 7107]. The other cluster corresponds to ∼4.4 MDa. In addition, a molecular mass of 4.1 MDa, determined by multiangle laser light scattering (MALLS), stands apart of the two clusters, separated from the masses obtained by other methods of molecular mass determination. We propose a stoichiometry of 192 globin and 36 linker chains for the 4.4-MDa molecule. The 36 linkers and 144 out of 192 globin chains are identified with the HBL and the remaining 48 globins are allotted equally to the two halves of the axial cavity above and below the central torus of the structure. The proposed model is supported by the occurrence in some annelid species of erythrocruorin with centrally placed subunits [Biochim. Biophys. Acta 359 (1974) 210], and by the oxidation-dependent shedding of subunits in Lumbricus erythrocruorin. We propose further that the 4.1 MDa determination represents the weight average molecular mass of a population of molecules resulting from a partial dissociation of 4.4-MDa erythrocruorin. This interpretation seems reasonable on the background of the very low protein concentrations (∼100 μg/ml and lower) prevailing at the MALLS experiment.

Original languageEnglish
Pages (from-to)1-15
Number of pages15
JournalBiochimica et Biophysica Acta - Proteins and Proteomics
Volume1649
Issue number1
DOIs
StatePublished - 26 Jun 2003

Keywords

  • Central subunit
  • Earthworm erythrocruorin
  • Earthworm hemoglobin
  • Lumbricus erythrocruorin
  • Lumbricus hemoglobin
  • Molecular mass

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