Roles of electrostatic interaction and polymer structure in the binding ofbeta-lactoglobulin to anionic polyelectrolytes: Measurement of binding constants by frontal analysis continuous capillary electrophoresis
T. Hattori et al., Roles of electrostatic interaction and polymer structure in the binding ofbeta-lactoglobulin to anionic polyelectrolytes: Measurement of binding constants by frontal analysis continuous capillary electrophoresis, LANGMUIR, 16(25), 2000, pp. 9738-9743
Frontal analysis continuous capillary electrophoresis was used to measure t
he binding of beta -lactoglobulin (BLG) to sodium poly( styrenesulfonate)(
PSS) and sodium poly( 2-acrylamido-2-methylpropanesulfonate) (PAMPS), two s
trong polyanions with similar linear charge densities. The binding isotherm
s obtained were well-fit by the McGhee -von Hippel equation, yielding the i
ntrinsic binding constant, K-obs, and the binding site size, n, representin
g the number of polymer segments per bound protein. Two opposite ionic stre
ngth (I) dependencies of K-obs for BLG-PSS were found depending upon pH, th
at is, increase of K-obs with I at pH 7.0, and decrease of K-obs, with I at
pH 6.3. The opposite I dependencies reflected the roles of electrostatic i
nteractions for systems with heterogeneously charged components, but also d
emonstrated the inapplicability of a simple formulation (log K-obs = log K-
o - Z(phi) log [M+]) put forward for the binding of protein to DNA. K-obs f
or PAMPS was always much smaller than that for PSS at equal pH. In addition
, n for BLG-PSS was small and independent of I and pH, while n for PAMPS wa
s large and increased with I and pH, both results consistent with "tighter"
binding of BLG to PSS than to PAMPS. This marked contrast may arise from t
he effects of polymer persistence length or from hydrophobic interactions.