Chemical studies on the isolated collagen-like and globular fragment of complement component C1q. Comparative studies on bovine and human C1q.

Both the collagen-like and the globular fragments of a subcomponent C1q of the first component of bovine and human complement were highly purified by enzymic digestion followed by gel filtration. Analyses by polyacrylamide gel electrophoresis showed that the former was composed of covalently linked peptide chains with an average molecular weight of 14 000, and that the latter was composed of three non-covalently linked peptide chains each having a molecular weight of approximately 15 000. Great similarities between amino acid compositions of the globular fragments and some similarities between those of the collagen-like fragments were found. Moreover, great similarities of amino acid compositions were found among three non-covalently linked chains of each globular fragment as well as between the corresponding chains of both globular fragments. These results suggested that both the collagen-like and the globular domains on the C1q molecule remained highly conserved in its evolution.