Tj. Su et al., THE CONFORMATIONAL STRUCTURE OF BOVINE SERUM-ALBUMIN LAYERS ADSORBED AT THE SILICA-WATER INTERFACE, JOURNAL OF PHYSICAL CHEMISTRY B, 102(41), 1998, pp. 8100-8108
The adsorption of bovine serum albumin (BSA) at the hydrophilic silica
-water interface has been studied using specular neutron reflection. T
he measurements were made over the concentration range from 0.005 to 0
.5 g dm(-3). The surface excess was found to vary from 1.8 to 2.4 mg m
(-2). The layers could be modeled using a single uniform layer model,
suggesting that over the concentration range studied then is insignifi
cant denaturation, which would lead to a more fragmented peptide distr
ibution and hence layers of different density. Comparison of the layer
thickness with the dimensions of the ellipsoidal structure of the glo
bular solution structure indicates that the molecules adsorb sideways-
on. Nevertheless, the layer thickness is always less than 40 Angstrom,
suggesting that adsorption onto the hydrophilic surface results in so
me structural deformation. The increase of layer thickness with bulk c
oncentration suggests that the extent of the distortion is reduced as
the lateral repulsion between protein molecules increases. The effect
of pH on the adsorbed BSA layer was examined by varying the pH at a fi
xed BSA concentration of 0.15 g dm(-3). The cycle was started at a pH
of 5.1, followed by pH 7, 5.1, 3, and then back to 5.1. The neutron re
flectivity profiles showed no hysteresis in either adsorbed amount or
structure. The reversibility of the adsorption of BSA with respect to
pH is consistent with no denaturation occurring on the surface. The ad
sorbed amount was a maximum at pH 5.1, which is close to the isoelectr
ic point at pH 4.8.