Physical properties of sponge aggregation factor. A unique proteoglycan complex

Physical properties of the aggregation factor isolated from the marine sponge Microciona parthena are described. The active molecular complex has an intrinsic viscosity of about 500 cm³/g and a sedimentation constant of 62 S. These results suggest a large, fibrous molecule of about 21 × 10⁵ daltons. Light scattering yields a similar molecular weight and a radius of gyration of 800 Å. These data, together with the electron microscopic images presented in the accompanying paper, indicate that the aggregation factor complex in solution has an open, sunburst structure with a diameter of 1600 Å or more. When Ca²⁺ ions are removed, the factor complex gradually dissociates into glycoprotein subunit molecules of 2 × 10⁵ daltons plus a core.