*4.2. Chemicals*

Tris(hydroxymethyl)aminomethane was from Mallinckrodt (Dublin, Ireland) and EDTA from Serva (Heidelberg, Germany). Urea and sodium carbonate were from Merck (Kenilworth, NJ, USA), while trypsin from bovine pancreas Type I, (~12,443 benzoyl L-arginine ethyl ester BAEE units/mg protein) was from Sigma (Darmstadt, Germany).

#### *4.3. Isolation of Insoluble Collagen, Intercellular Collagen, and Spongin-Like Collagen*

Sponge specimens were chopped and foreign inorganic and organic material was removed before washing with tap water. Before further processing the sponge tissues were immersed in EtOH for 24 h. InSC was isolated using an alkaline denaturing homogenization buffer (0.1 M Tris-HCl, pH 9.5, 0.01 M EDTA, 8 M urea, 0.1 M 2-mercaptoethanol), as previously described [24,26], whereas ICC and SlC were isolated using a trypsin-containing extraction buffer (0.1% trypsin in 0.1 M bicarbonate buffer, pH 8.0) [22,23]. All collagen samples were collected after centrifugation (at 20,000× *g* and 50,000× *g*, respectively) and lyophilization.
