The Interaction of Lysozyme with Carrageenans

Resumo

The interaction of lysozyme with kappa and lambda carrageenans and the thermal stability of the enzyme within a complex are studied via turbidimetry, dynamic light scattering, and differential scanning calorimetry. It is shown that complexes of lysozyme with kappa carrageenan are stabilized by Coulomb and secondary forces, while the complex formation of lysozyme with lambda carrageenan is governed by electrostatic interactions only. The stoichiometric composition of the complexes at a pH of 7.0 and an ionic strength of I = 0.01 is 0.3 : 1.0 (weight of carrageenan/weight of lysozyme) or 1 : 120 (mole of carrageenan/mole of lysozyme) and changes monotonically with an increase in I up to a higher carrageenan content in the mixture. The effect of I on the complex formation has a nonmonotonic character at q = 0.1 and q = 0.3. The complex formation is accompanied by the loss of thermal stability of the enzyme (which is more significant in the case of lambda carrageenan), suggesting that carrageenans have a higher affinity for the unfolded form of lysozyme than for its native form.