Affinity chromatography of porcine pepsin A using quinolin-8-ol as ligand

Determination of pepsin by capillary electrophoresis using mixed polymer coated capillary with switchable properties towards protein adsorption/desorption

In this work, a simple on-line preconcentration method for quantitative detection of pepsin was realized by using the binary mixed polymer brushes coated capillary with switchable properties towards protein adsorption. Firstly, the binary mixed polymer brushes were prepared by grafting poly(2-methyl-2-oxazoline) and poly(4-vinylpyridine) onto the inner wall of the capillary through polydopamine anchor. Then the coatings were characterized by X-ray photoelectron spectrometer and electroosmotic flow measurement. The results indicated that the composition of coating could be controlled by varying the feed ratio of poly(2-methyl-2-oxazoline) to poly(4-vinylpyridine) and the inner surface charge could be tuned toward the change of pH and ionic strength. The results showed when poly(2-methyl-2-oxazoline)/poly(4-vinylpyridine) mass ratio was 80/20, the highest on-line preconcentration effect was obtained and the sensitivity enhancement factor was 6.3. Moreover, satisfactory sensitivity (limit of detection: 7.5 ng/mL) and good repeatability were obtained with on-line preconcentration method. The polymer coated capillary was still stable for on-line preconcentration and detection of pepsin after 50 consecutive runs. Lastly, the proposed method was used successfully to on-line preconcentrate pepsin in saliva matrix. This article is protected by copyright. All rights reserved.

Protein binding-induced surfactant aggregation variation: a new strategy of developing fluorescent aqueous sensor for proteins

Novel strategies of developing fluorescent sensors for proteins are highly demanded. In this work, we particularly synthesized a cholesterol-derivatized pyrene probe. Its fluorescence emission is effectively tuned by the aggregation state of a cationic surfactant dodecyltrimethylammonium bromide (DTAB). The used probe/DTAB assemblies exhibit highly sensitive ratiometric responses to pepsin and ovalbumin egg (o-egg) with detection limits of 4.8 and 18.9 nM, respectively. The fluorescence changes indicate the protein-surfactant interaction leads to further aggregation of DTAB assemblies. The results from Tyndall effect and dynamic light scattering verify this assumption. The responses to pepsin and o-egg are due to their strong electrostatic or hydrophobic interaction with DTAB assemblies at pH 7.4. The present noncovalent supramolecular sensor represents a novel and simple strategy for sensing proteins, which is based on the encapsulated fluorophore probing the aggregation variation of the surfactant assemblies.

Effect of the matrix structure and concentration of polymer-immobilized Ni2+–iminodiacetic acid complexes on retention of IgG1

Terpolymer bead particles (100-350 microm in diameter) were prepared by suspension radical polymerization from methacrylate esters [2,3-epoxypropyl methacrylate (GMA), 2-(2-hydroxyethoxy)ethyl methacrylate (DEGMA) and ethylene dimethacrylate (EDMA)] and subsequently derivatized affording iminodiacetic acid (IDA) chelating sorbents. The sorbents differed in pore volumes (0-0.7 cm3/g) and specific surface areas (0.03-9.8 m2/g) of their matrices as well as in the amounts of immobilized Ni2+-IDA complexes (0.03-1.58 mmol/g). The binding of imidazole was studied by frontal chromatography to evaluate the accessibility of Ni2+-IDA complexes. It was found that an increase in the bonded imidazole content with increasing immobilized Ni2+-IDA concentration was strongly dependent on the matrix morphology. A higher pore volume of the matrix significantly improved the utilizability of Ni2+-IDA complexes for imidazole binding. The performance of the sorbents based on two porous matrices with immobilized Ni2+-IDA concentration (0.1-1.58 mmol/g) differing in pore size distributions was compared in immobilized metal affinity chromatography (IMAC) of monoclonal mouse immunoglobulin IgG1 specific against human choriogonadotropic hormone (GTH-spec IgG1). The results have shown that sorbents based on matrix with large pores (up to 20 microm in diameter) exhibited high protein binding capacities. The GTH-spec IgG1 (Mw=158,000) was eluted from all the sorbents in its native form as was confirmed by MALDI-TOF.