Mr. Housaindokht et al., INTERACTION OF GLUCOSE-OXIDASE WITH IONIC SURFACTANTS - A MICROCALORIMETRIC STUDY, International journal of biological macromolecules, 15(6), 1993, pp. 337-341
The enthalpies of interaction of glucose oxidase at 25-degrees-C with
a homologous series of n-alkyltrimethylammonium bromides (TABs) at pH
10 and a homologous series of n-alkylsulfates at pH 3.2 have been meas
ured by microcalorimetry. For the n-dodecyl member of each series, DTA
B and sodium n-dodecylsulfate (SDS), the binding of the surfactants to
glucose oxidase as measured by equilibrium dialysis has been used in
combination with the enthalpy data to obtain the Gibbs energy (DELTAG(
vBAR)), enthalpy (DELTAH(vBAR)) and entropy (DELTAS(vBAR)) of binding
per surfactant molecule as a function of the number of surfactant mole
cules bound (vBAR). The thermodynamic parameters for the glucose oxida
se interaction with DTAB at pH 10 and SDS at pH 3.2 are very similar a
nd show that the interactions are entropically driven. The observed en
thalpies of interaction of glucose oxidase with the homologous n-alkyl
sulfates have been analysed in terms of the interactions between the a
nionic surfactant head group and cationic sites on the protein, hydrop
hobic binding and the thermal contributions arising from protein unfol
ding. At surfactant concentrations of 0.5 c.m.c., the enthalpy of unfo
lding of glucose oxidase is estimated to be 3610 +/- 560 kJ mol-1.