Interaction of the Physiological Tripeptide Glutathione with Colloidal Alumina Particles

Understanding of the molecular interactions of alumina particles with biomolecules is fundamental for a variety of biotechnological processes. To study the interactions of polypeptides with alumina particles, we have investigated the adsorption and desorption behavior of the physiologically relevant tripeptide glutathione (GSH, γ-glutamylcysteinylglycine) onto colloidal α-alumina particles (CPs). The adsorption of GSH to positively charged alumina particles was rapid, increased proportionally to the concentration of CPs, and shifted the isoelectric point of the CP to a less alcaline pH. Desorption of particle-bound GSH was achieved by increasing the ionic strength after adding salt to the suspension, suggesting that adsorption of GSH to alumina is governed by electrostatic interactions. The presence of negatively charged and GSH-structurally related molecules such as glutamate, γ-glutamylcysteine, γ-glutamylglutamate, or methyl-S-GSH prevented the binding of GSH to the positively charged alumina surface in a concentration dependent manner, while positively charged and net-uncharged molecules and GSH esters did not affect GSH adsorption to alumina CPs. These data suggest that exclusively electrostatic interaction via the carboxylate groups of GSH governs its binding to alumina particles

Adsorption and Orientation of the Physiological Extracellular Peptide Glutathione Disulfide on Surface Functionalized Colloidal Alumina Particles

Understanding the interrelation between surface chemistry of colloidal particles and surface adsorption of biomolecules is a crucial prerequisite for the design of materials for biotechnological and nanomedical applications. Here, we elucidate how tailoring the surface chemistry of colloidal alumina particles (<i>d</i>₅₀ = 180 nm) with amino (−NH₂), carboxylate (−COOH), phosphate (−PO₃H₂) or sulfonate (−SO₃H) groups affects adsorption and orientation of the model peptide glutathione disulfide (GSSG). GSSG adsorbed on native, −NH₂-functionalized, and −SO₃H-functionalized alumina but not on −COOH- and −PO₃H₂-functionalized particles. When adsorption occurred, the process was rapid (≤5 min), reversible by application of salts, and followed a Langmuir adsorption isotherm dependent on the particle surface functionalization and ζ potential. The orientation of particle bound GSSG was assessed by the release of glutathione after reducing the GSSG disulfide bond and by ζ potential measurements. GSSG is likely to bind via the carboxylate groups of one of its two glutathionyl (GS) moieties onto native and −NH₂-modified alumina, whereas GSSG is suggested to bind to −SO₃H-modified alumina via the primary amino groups of both GS moieties. Thus, GSSG adsorption and orientation can be tailored by varying the molecular composition of the particle surface, demonstrating a step toward guiding interactions of biomolecules with colloidal particles