Correlation between Serine and Thermal Stability of Collagen

Abstract

THE first suggestions of a correlation between the thermal shrinkage of collagen and its amino-acid composition were made by Takahashi and Tanaka¹ and Gustavson^2,3. They found that the shrinkage temperature (T_S) increased with the amount of hydroxyproline, and interpreted this as being a result of the hydrogen-bonding capacity of the hydroxyl group of this imino-acid. Later work, in particular that of Piez and Gross⁴, has shown that T_S correlates equally well with proline content and that the sum of these two imino-acids gives the best correlation. Other workers^5,6 have shown that the melting point of tropocollagen molecules in dilute solution (T_D) varies in the same way with proline plus hydroxyproline. Regression coefficients obtained by Piez and Gross⁴ for plots of T_S versus proline plus hydroxyproline indicate that these residues contribute equally to the thermal stabilization of the molecule and the bulk material, that is, it seems that hydroxyproline is either not hydrogen-bonded or, if it is, its contribution is negligible. It is thought that the basis of this correlation is the steric hindrance to rotation of one imino-acid residue with respect to another imino-acid residue when they are in adjacent positions along a chain^7,8. In addition, Leach⁹ has pointed out that for the collagens he examined (serine plus threonine) appears to decrease with increase in T_S, while the sum of the hydroxyamino-acid (serine, tyrosine, threonine and hydroxyproline) remains approximately the same.