Collagen fibrillogenesis in the presence of lanthanides

Following removal of most of the telopeptide regions with pepsin, bovine dermal collagen gelled more slowly to form fibrils with a weak banding pattern. The reduction in gelling rate reflected an increase in the length of the nucleation phase and a lower rate of turbidity increase during the growth phase; the activation energy of both phases was increased. Lanthanide ions, phosphate, or, to a lesser degree, Ca²⁺ restored higher gelling rates to pepsin-treated collagen, but were unable to improve the banding pattern. Only lanthanide ions were able to accelerate the polymerization of intact collagen, lowering the activation energies of both the nucleation and growth phases. Lanthanide ions and phosphate also improved the banding characteristics of fibrils formed from intact collagen, without changing their width. Luminescence studies confirmed the direct binding of Tb³⁺ to collagen and suggested that the lanthanide ions may mediate their effects on fibrillogenesis by attaching to the helical part of the molecule. Quantitative considerations indicate that five or less lanthanide ion-binding sites per collagen molecule may be involved in the promotion of fibril formation.