Characterization of Cardiac Muscle Collagen

Connective tissue, composed of approximately 80 % collagen, has been isolated from cardiac muscle. Physicochemical studies of the soluble collagen from this source revealed an α1:α2 ratio of 14:1, a ratio far in excess of that required for molecules of the chain composition [α1(I)]2α2, suggesting that at least some of these α1 chains must be derived from molecules composed of three identical chains. This conclusion was substantiated by the isolation from cardiac collagen treated either with pepsin or papain of an α1 chain readily differentiated from the α1(I) chain. The cardiac collagen α1 chain had a molecular weight of 94,000 and an amino acid composition which indicated that the synthesis of this chain was directed by a different structural gene from that responsible for α1(I) synthesis. Characterization of the cyanogen bromide peptides from intact cardiac collagen revealed the presence of several peptides homologous to those derived from the α1(I) chain as well as peptides having no obvious homologs in digests of α1(I), indicating that cardiac muscle collagen is composed of a mixture of molecules having the chain composition [α1(I)]2α2, and (α1)3. The stoichiometry of the CNBr peptides suggested that at least 50 % of the cardiac muscle collagen was of the (α1)3 type. The cardiac α1 chain contained eight residues of hexose with a molar ratio of galactose to glucose of 3:1. Approximately 50 % of the hydroxylysine residues were substituted by hexose. The banding pattern of segment long-spacing aggregates from cardiac muscle collagen molecules was indistinguishable from that found for [α1(I)]2α2 molecules from calf skin. The enthalpy of thermal denaturation, however, was reduced, indicating that the tertiary superhelix structure of cardiac collagen is less stable than that from other collagen sources.