Enzyme activity electrophoresis: development and applications

Screening of angiotensin converting enzyme inhibitors from natural products via origami microfluidic paper-based analytical devices with colorimetric detection

We report the screening of angiotensin converting enzyme (ACE) inhibitors on an origami microfluidic paper-based analytical device (μPAD) using colorimetric detection. The hydrolysis product reacts with ninhydrin, resulting in a purple color at the detection zones. Images of the μPADs are captured using a common cell phone and analyzed with Photoshop software. This platform allows six independent colorimetric reactions to take place simultaneously, and the IC50 values can be obtained in a single run within 22 min. The relative standard deviations of inhibition efficiencies are generally lower than 4.0 % (n = 5). The IC50 values of captopril and five products from natural plants were obtained and corresponded well with UV methods. The relative deviations between the two methods are within the range of -5 % to +5 %. This work is a proof-of-concept successfully demonstrating the use of μPADs technology to screen enzyme inhibitors from natural products.

Immobilized metal ion affinity electrophoresis. A study with several model proteins containing histidine

Immobilized metal ion affinity electrophoresis (IMA-Elec) is one among the many methods derived from the immobilized metal ion affinity chromatography. Two approaches for incorporating the metal ligand, were studied. One was in the form of insoluble particulate material based on Sepharose 6B and the other in the form of soluble polymer based on polyethylene glycol (PEG) 5000. Both the polymers coupled with iminodiacetate and metallized with copper or zinc were used as ligands, incorporated into soluble agarose as the electrophoretic gel. Several histidine-containing model proteins were studied with both the systems and their metal binding strengths were determined as the dissociation constants, Kd. The results clearly demonstrated that the mechanism of protein recognition by immobilized copper or zinc via the accessible histidyl residues was maintained in the IMA-Elec system. Proteins with increasing numbers of histidine residues showed increasing binding strength (lower Kd values). While this basic mechanism was conserved, the supporting polymers (Sepharose 6B and the PEG 5000) showed significant differences in the metal binding to the protein. The polysaccharide Sepharose 6B enhanced the binding strength compared with PEG 5000. The optimum electrophoretic parameters were determined to be current intensities up to 20 mA and pH ca. 7.0. At pH greater than 8.0, a significant decrease in the affinity was observed, this decrease being greater with PEG 5000 than Sepharose 6B as supporting material.

Immobilized metal ion affinity electrophoresis: a preliminary report

The ligand "Sepharose-IDA-Cu(II)" was entrapped into an agarose gel used for affinity electrophoresis. The binding of three closely related proteins, namely alpha-chymotrypsinogen A, alpha-chymotrypsin, and alpha-chymotrypsin inactivated with diisopropyl fluorophosphate (DIFP) to the affinity gel, was investigated. When the protein having affinity for the ligand was run in the presence of small amounts of the ligand, the retention of the protein by the ligand caused "tailing" of the sample. This pattern was changed in the presence of increasing amounts of the ligand, leading to a "rocket" shape due to the stronger binding of the protein to the chelated metal ligand entrapped in the gel. The degree of retardation in the gel with the ligand is an expression of the affinity between the protein and the ligand. The migration distance of alpha-chymotrypsin and alpha-chymotrypsin treated with DIFP at a given concentration of the ligand is linearly related to the protein amount deposited on the gel. The dissociation constant for the tested proteins were calculated from the Bøg-Hansen-Takeo plot. The difference in the affinity strength of these structurally related proteins towards the ligand suggests the involvement of the surface topography of histidine residues on their binding to the ligand.

Cationic detergent in agarose for improved electrophoresis of cationic proteins

Inclusion of the cationic detergent N-cetyl-N,N,N-trimethylammonium bromide (CTAB) in normal agarose gels increases the electrophoretic separation and banding pattern of cationic proteins. This is shown for an extract of cationic granular proteins from polymorphonuclear granulocytes.