STRUCTURAL AND CHEMICAL STUDIES ON THE CONNECTIVE TISSUE OF MARINE SPONGES

1. The mesoglea of the marine sponge, S. graminea, resembles in its organization and composition the connective tissue of vertebrates in that it is composed of collagen fibers and fibrils embedded in an amorphous matrix containing carbohydrates. 2. Two morphologically distinct forms of spongin fibers, designated spongin "A" and spongin "B", were demonstrated to be members of the collagen class, structurally by x-ray diffraction and electron microscopy, and chemically by their hydroxyproline and glycine content as well as by the general amino acid pattern. Ratios of glycine to hydroxyproline were 1.6 and 1.8 for spongin "A" and "B" respectively. Spongin "A" is a long unbranched fibril of uniform width, of the order of 200 A revealing an axial period of 625 A by small-angle x-ray diffraction and of about 650 A by electron microscopy. Spongin "B" is a large branched fiber 10-50 µ in width composed primarily of bundles of thin unbranched filaments less than 100 A wide. "B" fiber fragments occasionally showed an axial period in the collagen range although x-ray preparations did not yield a low-angle pattern. 3. Content of hexosamine, hexose, pentose and uronic acid was determined in both fiber types and in the amorphous matrix. Glucosamine, galactosamine, glucose, galactose, mannose, fucose, arabinose and uronic acid were identified chromatographically in both spongin "A" and in the amorphous substance. A very small amount of amino sugar plus glucose and galactose were identified in spongin "B". All sugars with the exception of arabinose are found in mammalian skin connective tissue. 4. Spongins "A", "B" and the amorphous matrix were readily separated by tryptic digestion and water extraction.