title: Interactions and diffusion in fine-stranded β-lactoglobulin gels determined via FRAP and binding.
abstract: The effects of electrostatic interactions and obstruction by the microstructure on probe diffusion were determined in positively charged hydrogels. Probe diffusion in fine-stranded gels and solutions of β-lactoglobulin at pH 3.5 was determined using fluorescence recovery after photobleaching (FRAP) and binding, which is widely used in biophysics. The microstructures of the β-lactoglobulin gels were characterized using transmission electron microscopy. The effects of probe size and charge (negatively charged Na2-fluorescein (376Da) and weakly anionic 70kDa FITC-dextran), probe concentration (50 to 200 ppm), and β-lactoglobulin concentration (9% to 12% w/w) on the diffusion properties and the electrostatic interaction between the negatively charged probes and the positively charged gels or solutions were evaluated. The results show that the diffusion of negatively charged Na2-fluorescein is strongly influenced by electrostatic interactions in the positively charged β-lactoglobulin systems. A linear relationship between the pseudo-on binding rate constant and the β-lactoglobulin concentration for three different probe concentrations was found. This validates an important assumption of existing biophysical FRAP and binding models, namely that the pseudo-on binding rate constant equals the product of the molecular binding rate constant and the concentration of the free binding sites. Indicators were established to clarify whether FRAP data should be analyzed using a binding-diffusion model or an obstruction-diffusion model.
authors.affiliation: Department of Structure and Material Design, Swedish Institute for Food and Biotechnology, SIK, Göteborg, Sweden; SuMo BIOMATERIALS, VINN Excellence Center, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: Erich
authors.initials: E
authors.lastname: Schuster
authors.affiliation: Department of Structure and Material Design, Swedish Institute for Food and Biotechnology, SIK, Göteborg, Sweden; SuMo BIOMATERIALS, VINN Excellence Center, Chalmers University of Technology, Göteborg, Sweden; Department of Applied Surface Chemistry, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Hermansson
authors.affiliation: Department of Structure and Material Design, Swedish Institute for Food and Biotechnology, SIK, Göteborg, Sweden; SuMo BIOMATERIALS, VINN Excellence Center, Chalmers University of Technology, Göteborg, Sweden.
authors.forename: Camilla
authors.initials: C
authors.lastname: Ohgren
authors.affiliation: SuMo BIOMATERIALS, VINN Excellence Center, Chalmers University of Technology, Göteborg, Sweden; Mathematical Sciences, Chalmers University of Technology, and the University of Gothenburg, Göteborg, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Rudemo
authors.affiliation: Department of Structure and Material Design, Swedish Institute for Food and Biotechnology, SIK, Göteborg, Sweden; SuMo BIOMATERIALS, VINN Excellence Center, Chalmers University of Technology, Göteborg, Sweden. Electronic address: niklas.loren@sik.se.
authors.forename: Niklas
authors.initials: N
authors.lastname: Lorén
mesh_terms: D000818:Animals; D002417:Cattle; D004058:Diffusion; D036681:Fluorescence Recovery After Photobleaching; D020100:Hydrogels / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D055672:Static Electricity
chemical_list: D020100:Hydrogels; D007782:Lactoglobulins