Biochemical and Morphological Studies on Collagens of Horny Sponges. Ircinia Filaments Compared to Spongines

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Abstract
Three kinds of fibers with a widely different morphology were isolated from several species of horny sponges: (a) intercellular collagen fibrils (spongin A of Gross3); (b) spongin fibers (spongin B3); and (c) a distinct filament present only in Ircinia. In the last two fibers elementary fibrils can be distinguished under the electron microscope which are densely packed in spongin fibers and helically coiled and surrounded by an amorphous cuticule in Ircinia filaments8. The chemical composition of these three fibers was studied by comparing their nitrogen, iron, hexose, hexosamine and amino acid composition. The collagenous nature of Ircinia filaments was confirmed by their amino acid composition and by the presence of glycosyl galactosyl hydroxylysine. Compared to spongin fibers and to intercellular collagen fibrils the Ircinia filaments show some significant differences. Like spongin, the Ircinia filaments contain less threonine and serine and show a lower degree of glycosylation of hydroxylysine than intercellular collagen. Ircinia filaments and spongin resisted heating to 90° in 5% trichloroacetic acid. On the other hand intercellular collagen was “solubilized” under these conditions as vertebrate collagens. The kinetics of “solubilization” of spongin fibers and Ircinia filaments were studied in water and in ethanolic KOH. The speed of hydrolysis of both fibers increased considerably in the presence of ethanol suggesting the importance of hydrophobic interactions in the stabilization of these fibers. Ircinia filaments were solubilized more rapidly than spongin fibers. The difference in alkali sensitivity of these two fibers may be related to their different tertiary and quaternary structure.