Steady-state kinetics and thermodynamics of the hydrolysis of beta-lactoglobulin by trypsin

Protein acidification and hydrolysis by pepsin ensure efficient trypsin-catalyzed hydrolysis

Enzyme-catalysed hydrolysis is important in protein digestion. Protein hydrolysis is initiated by pepsin at low pH in the stomach. However, pepsin action and acidification happen simultaneously to gastric emptying, especially for liquid meals. Therefore, different extents of exposure to the gastric environment change the composition of the chyme that is emptied from the stomach into the small intestine over time. We assessed the susceptibility of a protein to trypsin-catalysed hydrolysis in the small intestine, depending on its pH and hydrolysis history, simulating chyme at different times after the onset of gastric emptying. Isothermal titration calorimetry was used to study the kinetics of pepsin and trypsin-catalysed hydrolysis. Bovine serum albumin (BSA) that was acidified and hydrolysed with pepsin, showed the highest extent and most efficient hydrolysis by trypsin. BSA in the chyme that would be first emptied from the stomach, virtually bypassing gastric acidity and peptic action, reduced trypsin-catalysed hydrolysis by up to 58% compared to the acidified, intact protein, and 77% less than the acidified, pepsin-hydrolysate. The least efficient substrate for trypsin-catalysed hydrolysis was the acidified, intact protein with a specificity constant (k_cat/K_m) nearly five times lower than that of the acidified, pepsin-hydrolysate. Our results illustrate the synergy between pepsin and trypsin hydrolysis, and indicate that gastric hydrolysis increases the efficiency of the subsequent trypsin-catalysed hydrolysis of a model protein in the small intestine.

Synthesis and controlled-release properties of chitosan/β-Lactoglobulin nanoparticles as carriers for oral administration of epigallocatechin gallate

A nano-sized double-walled carrier composed of chitosan and β-lactoglobulin (β-Lg) for oral administration of epigallocatechin gallate (EGCG) was developed to achieve a prolonged release of EGCG in the gastrointestinal tract. Carboxymethyl chitosan (CMC) solution was added dropwise to chitosan hydrochloride (CHC) containing EGCG to form a primary coating by ionic complexation. Subsequently, β-Lg was added to create a secondary layer by ionic gelation. The obtained EGCG-loaded chitosan/β-Lg nanoparticles had sizes between 100 and 500 nm and zeta potentials ranging from 10 to 35mV. FT-IR spectroscopy revealed a high number of hydrogen-bonding sites in the nanoparticles, which could incorporate EGCG, resulting in high encapsulation efficiency. EGCG incorporated in the primary coating was released slowly over time by diffusion from the swollen CMC-CHC matrix after the outer layer of β-Lg was degraded in the intestinal fluid. The sustained-release property makes chitosan/β-Lg nanoparticles an attractive candidate for effective delivery of EGCG.

Fluorescence anisotropy assay for proteolysis of specifically labeled fusion proteins

A cloning method and plasmid vectors that permit fluorescence-anisotropy-based measurement of proteolysis are reported. The recombinant protein substrates produced by this method contain a tetracysteine motif that can be site-specifically labeled with bis-arsenical fluorophore [Science 281 (1998) 269]. Six protein substrates with an N-terminal fusion of the tetracysteine motif and different protease recognition sites were created and tested for reaction with commercial proteases commonly used to process recombinant fusion proteins. In each case, proteolysis of a single susceptible peptide bond could be monitored in real time and with sufficient data quality to allow numerical analysis of proteolysis reaction kinetics. Measurement of proteolysis extent using fluorescence anisotropy is shown to be comparable to densitometry measurements made on denaturing polyacrylamide gels but with the added advantages implicit in a time-resolved measurement, quantification by a spectroscopic measurement, and facile extensibility to high-throughput formats. The assay was also demonstrated as a general tool for monitoring proteolysis of multidomain fusion proteins containing an internal protease site such as are being created in structural genomics studies worldwide.

Effective experimental design: enzyme kinetics in the bioinformatics era

Acquiring details about the kinetic parameters of enzymes is crucial to both drug development and clinical diagnosis. The correct design of an experiment is crucial to collecting data suitable for analysis, modelling and deriving the correct information. As classical design methods are not targeted to the more complex kinetics now frequently studied, further work is required to estimate parameters of such models with low variance. This review examines the different options available to produce major gains in information, productivity and the accuracy of each experiment.

Studies of reversible inhibition, irreversible inhibition, and activation of alkaline phosphatase by capillary electrophoresis

Reversible inhibition, irreversible inhibition, and activation of calf intestinal alkaline phosphatase (EC 3.1.3.1) have been studied by capillary electrophoresis. The capillary electrophoretic enzyme-inhibitor assays were based on electrophoretic mixing of inhibitor and enzyme zones in a substrate-filled capillary. Enzyme inhibition was indicated by a decrease in product formation detected in the capillary by laser-induced fluorescence. Reversible enzyme inhibitors could be quantified by Michaelis-Menten treatment of the electrophoretic data. Reversible, competitive inhibition of alkaline phosphatase by sodium vanadate and sodium arsenate has been examined, and reversible, noncompetitive inhibition by theophylline has been studied. The K(i) values determined for these reversible inhibitors using capillary electrophoresis are within the range of values reported in the literature for the same enzyme-inhibitor combinations. Irreversible inhibition of alkaline phosphatase by EDTA at concentrations of 1.0mM and above has been observed. Activation of alkaline phosphatase has also been observed for EDTA at concentrations from 20 to 400 microM.