The molecular weight and subunit organization of Helisoma trivolvis (Say) hemoglobin: light-scattering and scanning transmission electron microscopic studies.

Abstract The hemoglobin of the freshwater snail, Helisoma trivolvis has a molecular weight of 1.77(± 0.04) × 10 6 Da as determined by light-scattering measurements at 630 nm. Scanning transmission electron microscopic measurements gave nearly the same particle mass of 1.85(± 0.24) × 10 6 Da. The molecular weight of the denatured hemoglobin in 6.0 M GdmCl is found to be 3.96 × 10 5 Da, which is close to one-fifth of the mass of the parent hemoglobin. The molecular weight data based on light-scattering and STEM microscopy is consistent with a 10-subunit structure comprising five disulfide-linked dimers, as opposed to a 12-subunit assembly proposed by Ilan et al . (1986), which would necessitate a higher particle mass. Analysis of the molecular weight and the sedimentation data of H. trivolvis hemoglobin, suggests a compact two-layer ring structure of decamers of about 200 A to 250 A diameter, stabilized by disulfide-linkages between the subunits of the two pentameric layers.