Circular Dichroism Analysis of the Effect of Metallic Ions on Structure of Collagen Molecules

Circular dichroism spectroscopy was used to study the effect of metallic ions such as Fe 3+,Al 3+and Ca 2+on the structure of collagen molecules.The results showed the effect of the ions was similar to that of thermal denaturation but not as strong.On the basis of the obtained results,the mechanism used by the metallic ions to protect the biovalves from calcification may be explained as follows.Collagen is the dominant component of the biovalves.Pretreating the biovalves with glutaraldehyde caused many amino acid residues in collagen molecules to cross link.This leads to a decrease in the total positive charge in the collagen molecules and a relative surplus of free carboxyl groups.The trivalent metallic ions such as Fe 3+preferentially bound with negatively charged carboxyl groups of collagen molecules,which caused the superhelix of the collagen to be loose and random.This improved the mechanical properties of the biovalve and neutralized surplus free carboxyl groups caused by the glutaraldehyde treatment,closed the sites where the Ca 2+was bound.Also,it effectively protected the biovalves from calcification.