Interaction between fatty acid salts and elastin: Kinetics, absorption equilibrium, and consequences for elasticity

Elastin from bovine ligamentum nuchae is incubated in aqueous solutions of sodium salts of fatty acids (FAS). The FAS are laurate, myristate, and palm itate. Absorption of FAS in the elastin network is studied as a function of time, FAS concentration, and ionic strength. The consequences of this upta ke for the elasticity of the elastin are studied by static and dynamic stre ss-strain measurements. Generally distinction must be made between the init ial time-dependent stage (I) and the final equilibrium stage (II). In I the initial rate of absorption follows a second-order binding mechanism, with the rate constant increasing with decreasing length of the FAS. In this reg ime, die elasticity modulus remains more or less unaffected. Especially in regime II the absorption of FAS is enhanced by a reduction ib the cross-lin k density in the elastin network. This is ascribed to an osmotic pressure p rimarily caused by the concomitant uptake of low molecular weight ions in t he elastin. The absorption equilibrium can be described by Langmuir theory. The absorption affinity increases with increasing hydrocarbon chain length of the FAS, indicating the contribution of hydrophobic interaction. Althou gh the elasticity is not lost, the modulus is now reduced and a concomitant viscous component is developed. (C) 1999 John Wiley & Sons, Inc.