Kinetic analysis of an enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

An in-line method for high-throughput screening of protein tyrosine phosphatase receptor type O inhibitors by capillary electrophoresis based on electrophoretically mediated microanalysis

Protein tyrosine phosphatase receptor type O (PTPRO) plays an important role in inflammation-related pathways and has become an emerging drug target. In this study, we developed an in-line capillary electrophoresis (CE) method for the investigation of the enzymatic activity of PTPRO, which was based on electrophoretically mediated microanalysis (EMMA). After a thorough method validation of the optimized conditions, this protocol was successfully employed to determine the kinetics of PTPRO as well as the half-maximal inhibitory concentration (IC50) of two typical PTPRO inhibitors. The final results were consistent with the values obtained through classical ultraviolet-visible (UV-vis) spectrophotometry. Our new method exhibited improved accuracy and reduced consumption, avoiding the disadvantages of traditional methods. This work provides a new strategy for PTPRO enzyme kinetic studies as well as inhibitory activity determination through capillary electrophoresis for the first time.

Kinetic analyses of two-steps oxidation from l-tyrosine to l-dopaquinone with tyrosinase by capillary electrophoresis/dynamic frontal analysis

Tyrosinase catalyzes the oxidation of l-tyrosine in two stages to produce l-dopa and l-dopaquinone stepwise, and l-dopaquinone is subsequently converted to dopachrome. Most of the conventional analyses subjected only one-step reaction from l-tyrosine to l-dopa or from l-dopa to l-dopaquinone. In this study, kinetic analyses of two-steps oxidation of l-tyrosine with tyrosinase were made by capillary electrophoresis/dynamic frontal analysis (CE/DFA). When l-dopa was introduced into a capillary as a sample plug in a CE/DFA format, the enzymatic oxidation continuously occurred during the electrophoresis, and the product l-dopaquinone was subsequently converted to dopachrome which was detected as a plateau signal. A Michaelis-Menten constant of the second-step kinetic reaction, K_m,Do, was determined as 0.45 ± 0.03 mmol L^-1. In the analysis of the first-step kinetic reaction from l-tyrosine to l-dopa, l-dopa was not resolved by CE/DFA because both l-tyrosine and l-dopa are electrically neutral. The l-dopa formed and co-migrated at the l-tyrosine zone was calibrated beforehand with the final product of dopachrome detected as a plateau signal. Constantly formed l-dopa was successfully detected as a plateau signal of dopachrome, and a Michaelis-Menten constant of K_m,Ty was also determined as 0.061 ± 0.009 mmol L^-1 by the CE/DFA. CE/DFA is applicable to two-steps enzymatic reactions.

Esterase Activity of Serum Albumin Studied by 1H NMR Spectroscopy and Molecular Modelling

Serum albumin possesses esterase and pseudo-esterase activities towards a number of endogenous and exogenous substrates, but the mechanism of interaction of various esters and other compounds with albumin is still unclear. In the present study, proton nuclear magnetic resonance (1H NMR) has been applied to the study of true esterase activity of albumin, using the example of bovine serum albumin (BSA) and p-nitrophenyl acetate (NPA). The site of BSA esterase activity was then determined using molecular modelling methods. According to the data obtained, the accumulation of acetate in the presence of BSA in the reaction mixture is much more intense as compared with the spontaneous hydrolysis of NPA, which indicates true esterase activity of albumin towards NPA. Similar results were obtained for p-nitophenyl propionate (NPP) as substrate. The rate of acetate and propionate release confirms the assumption that there is a site of true esterase activity in the albumin molecule, which is different from the site of the pseudo-esterase activity Sudlow II. The results of molecular modelling of BSA and NPA interaction make it possible to postulate that Sudlow site I is the site of true esterase activity of albumin.

Overview of in-capillary enzymatic reactions using capillary electrophoresis

This review summarizes the research that has recently been performed on in-capillary enzymatic reactions integrated with capillary electrophoresis. The manuscript is subdivided in homogeneous and heterogeneous approaches. The main homogeneous techniques are Electrophoretically Mediated Microanalysis, At-inlet and Transverse Diffusion of Laminar Flow Profiles. The main heterogeneous ones are Immobilized MicroEnzyme Reactors with enzymes grafted on either non-magnetic or magnetic particles. The overview covers the period from 2018 to early 2021. The applications range from drug discovery over natural products to food, beverage and pesticide analysis.

Kinetic analysis of the transphosphorylation with creatine kinase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

Kinetic reactions of the transphosphorylation with creatine kinase (CK) were individually investigated between creatine (Cr) and creatine phosphate (CrP) by pressure-assisted capillary electrophoresis/dynamic frontal analysis (pCE/DFA). The transphosphorylations are reversible between Cr and CrP, and reverse reactions inevitably accompany in general batch analyses. In pCE/DFA, the kinetic reaction proceeds in a separation capillary and the product is continuously resolved from the substrate zone. Therefore, the formation rate is kept constant at the substrate zone without the reverse reaction, and the product is detected as a plateau signal. This study demonstrates the direct and individual analyses of both the forward and the backward kinetic reactions with CK by pCE/DFA. A plateau signal was detected in the pCE/DFA with ADP or ATP as one of the products on either the forward or the backward reactions. The Michaelis-Menten constants of K_m,ATP (from Cr to CrP) and K_m,ADP (from CrP to Cr) were successfully determined through the plateau signal. Determined values of K_m,ATP and K_m,ADP by pCE/DFA were smaller than the ones obtained by the pre-capillary batch analyses. The results agree with the fact that the reverse reaction is excluded in the analysis of the kinetic reactions. The proposed pCE/DFA is useful on individual analyses of both forward and backward kinetic reactions without any interference from the reverse reaction.