Adsorption kinetics and dilatational rheological studies for the soluble and anchored forms of alkaline phosphatase at the air/water interface

This work presents equilibrium and dynamic aspects for the adsorption at the air/liquid interface of two rat osseous plate alkaline phosphatase forms: DSAP, solubilized by a surfactant, C12E9), and containing a glycosylphosphatidylinositol (GPI) anchor; and PLSAP, resulting from phospholipase-C cleavage of the hydrophobic portion of the GPI anchor. Dynamic surface tension, gamma(dyn) and surface elasticity modulus, epsilon, were determined for PLSAP, DSAP and pure C12E9 solutions using harmonic oscillation and axisymmetric drop shape analysis Adsorption kinetics studies revealed that DSAP adsorbs thirty times faster than PLSAP, presenting a minimum in the curve. For DSAP/C12E9 mixed system, e increases with concentration and a maximum appears at the critical aggregation concentration (CAC). For PLSAP, a continuous decreasing with concentration for gamma(dyn) and epsilon was observed. For pure C12E9 Egsolution, the elasticity modulus increases with concentration and epsilon values are higher when compared to the mixed system. A model based on the influence of the GPI anchor is proposed.