Occurrence of fibrillar collagen with structure of (alpha(1))(2) alpha(2) in the test of sea urchin Asthenosoma ijimai

Test collagen from the sea urchin Asthenosoma ijimai was disaggregated into collagen fibrils in a neutral salt solution containing beta-mercaptoethanol, solubilized by limited pepsin digestion and isolated by selective precipitation with NaCl. The test collagen was mostly rendered soluble and found to consist of two distinct alpha-chains, alpha(1) and alpha(2), which could be isolated by CM-cellulose chromatography followed by Sepharose CL-4B gel filtration. Each of the alpha-chains had a molecular mass of about 100 kDa and the alpha(1)- and alpha(2)-chains existed in a molar ratio of about 2:1, indicating the occurrence of(alpha(1))(2) alpha(2) heterotrimers. This was confirmed by amino acid analyses of the isolated alpha-chains. From these results, the fibrillar collagen of sea urchin test appears to share common characteristics, such as precipitation properties with NaCl, chromatographic and electrophoretic behaviours and subunit composition with vertebrate type-I collagen. This type of fibrillar collagen was also found in other species of sea urchins.