THE MOLECULAR-WEIGHT AND SUBUNIT ORGANIZATION OF HELISOMA-TRIVOLVIS (SAY) HEMOGLOBIN - LIGHT-SCATTERING AND SCANNING-TRANSMISSION ELECTRON-MICROSCOPIC STUDIES

The hemaglobin of the freshwater snail, Helisoma trivolvis has a molec ular weight of 1.77(+/-0.04) x 10(6) Da as determined by light-scatter ing measurements at 630 nm. Scanning transmission electron microscopic measurements gave nearly the sam particle mass of 1.85(+/-0.24) x 10( 6) Da. The molecular weight of the denatured hemoglobin in 6.0 M GdmCl is found to be 3.96 x 10(5) Da, which is close to one-fifth of the ma ss of the parent hemoglobin. The molecular weight data based on light scattering and stem microscopy is consistent with a 10-subunit structu re comprising five disulfide-linked dimers, as opposed to a 12-subunit assembly proposed by Ilan et al. (1986), which would necessitate a hi gher particle mass. Analysis of the molecular weight and the sedimenta tion data of H. trivolvis hemoglobin, suggests a compact two-layer rin g structure of decamers of about 200 Angstrom to 250 Angstrom diameter s, stabilized by disulfide-linkages between the subunits of the two pe ntameric layers