Abstract
Acid-soluble collagens were extracted from the sea anemone Actinia equina and from the liver fluke Fasciola hepatica and purified by repeated reprecipitation. They share the following properties with collagens from highly developed animals: digestibility by collagenase; important characteristics of amino acid composition (one-third glycine, high imino acid content, presence of hydroxyproline and hydroxylysine); a firmly attached hexose moiety; sedimentation as an extremely sharp boundary in the native state; a high negative value for the specific optical rotation; the ability of forming cross-striated fibrils and segments as seen in the electron microscope. The molecular weight of the collagen from Actinia is in accord with that of vertebrate collagen (310,000). For the collagen isolated from Fasciola a higher value (500,000) was obtained. The subunits of the latter collagen were very labile and could not be characterized in the ultracentrifuge or by disc-electrophoresis. The length and the highly differentiated cross-striation pattern of the long spacing segments from the two invertebrate collagens were found to be identical with those of segments from calf skin collagen and carp swim bladder collagen. This indicates invariance of the tertiary and quaternary structures of the collagen molecule during evolution, and probably reflects also invariance of fundamental features of the amino acid sequence. Two further evolutionary aspects of collagen are discussed. Evidence for only one α-subunit was found in collagen from Actinia, whereas two or three are present in the collagens of highly developed animal phyla. This apparently confirms a hypothesis on the divergent evolution of the collagen α-chain gene. The thermal stability of the collagen molecule in solution depends on the environmental conditions of the animal from which the collagen was prepared. There is no relationship between this property, however, and the phylogenetic stage of the animal.
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