Species-specific aggregation factor in sponges. I. Characterization of the large circular proteid particle

We have isolated circular proteid particles (CPP) from the sponge Geodia cydonium, which carry the aggregation factor, and have freed them from concomitant impurities. The CPP have been visualized by electron microscopy as annular particles with a circular contour length of 3530 Å. The circles are surrounded by 25 filaments 610 Å in length. The CPP are characterized by a sedimentation coefficient (S°20,w) of 3000, by a buoyant density of 1.32 g/cm3 and by a particle weight of about 2–5 · 109 daltons. They consist primarily of protein. It is suggested that the fibrous complex found electron microscopically is only the core structure of a more complex particle.