Native and hydrophobically modified human immunoglobulin G at the air/water interface - Sequential and competitive adsorption

The adsorption of human immunoglobulin G (IgG) at the air/water interface w as monitored both by the in situ radiotracer technique using [C-14] labeled IgG and by surface tension measurements. The results reveal that adsorptio n of IgG from single protein systems displays bimodality due to molecular r earrangements at the interface. Above the threshold value of 1.5 x 10(-2) m g/ml solution concentration, adsorbed IgG molecules reoriented from the sid e-on to the end-on configuration. The existence of a lag time which did not appear in Gamma = f(t) curves, was observed in Pi = f(t) relationships at low protein concentrations and was due to the limits of the surface pressur e technique to detect protein adsorption. The adsorption of native IgG was also carried out in the presence of a hydrophobized IgG obtained by graftin g capryloyl residues to its lysine groups by reaction with N-hydroxysuccini mide ester of caprylic acid, which yielded 19 covalently bound alkyl chains to the IgG molecule (19C(8)-IgG). This modified IgG exhibited enhanced ads orption at the air/water interface, as manifested by its increased adsorpti on efficiency relative to the native protein. Sequential and competitive ad sorption experiments from binary mixtures of native IgG and 19C(8)-IgG clea rly demonstrate that the displacement of the native protein from the air/wa ter interface strongly depended on the manner of how 19C(8)-IgG and native IgG competed with each other. When the two proteins competed simultaneously , 19C(8)-IgG predominantly occupied the available area but when native Ige was adsorbed first, for 2 h, the sequentially adsorbed 19C(8)-IgG was incap able of substantially displacing it from the interface. (C) 2001 Academic P ress.