PHYSICAL CHEMICAL STUDIES ON AGE CHANGES IN RAT TAIL TENDON COLLAGEN

Collagen was solubilized from the tail tendons of rats of different ages in dilute acetic acid. Optical rotation measurements on the solubilized collagen indicated that no significant age changes occur in the overall secondary structure of collagen. Sedimentation velocity measurements on the solubilized collagen in KSCN solutions, in which the secondary structure is broken down, revealed only α (single-stranded) and β (double-stranded) subunits. The portion of α in the acid-solubilized collagen, measured by sedimentation velocity, decreases markedly between 1 and 3 months but remains fairly constant thereafter. The rate of solubilization and the fraction of the total collagen eventually solubilized, however, showed drastic changes after 3 months, but not before. These observations are in line with a continuing production of covalent crosslinks in the collagen fiber throughout the life span of the animal, according to the following kind of picture: β subunits are, effectively, first produced by crosslinking α subunits within the tropocollagen molecules laid down in the formation of the fiber. Crosslinking then spreads randomly within and between tropocollagen units, and eventually an insoluble matrix is built up, so that less and less solubilizable collagen becomes more and more entrapped. © 1968.