Time Evolution of Exposed Hydrophobicity of Water-Soluble Proteins During their Depolymerisation by Endo-Proteases

During the depolymerisation of a water-soluble protein by an endo-protease, the exposed hydrophobicity of the substrate, that is the hydrophobicity that is accessible to hydrophobic probes, changes with the progress of the reaction. This work describes the depolymerisation of bovine serum albumin, α-casein and β-lactoglobulin using the proteases Alcalase, Flavourzyme, α-chymotrypsin, mercuripapain and trypsin. Time evolution of substrate hydrophobicity was monitored by a flow-injection analysis (FIA) system with fluorescence detection and an aqueous eluant containing p-toluidinylnaphthalene-6-sulfonate (2,6-TNS) as the fluorescent probe. In all cases, the time evolution of the substrate hydrophobicity was fitted using a derived mathematical function containing two adjustable rate constants and two constant parameters. This methodology allowed the determination of protease activities, as well as online monitoring of the depolymerisation process, when using water-soluble proteins as substrate.

Flow-based systems for rapid and high-precision enzyme kinetics studies

Enzyme kinetics studies normally focus on the initial rate of enzymatic reaction. However, the manual operation of steps of the conventional enzyme kinetics method has some drawbacks. Errors can result from the imprecise time control and time necessary for manual changing the reaction cuvettes into and out of the detector. By using the automatic flow-based analytical systems, enzyme kinetics studies can be carried out at real-time initial rate avoiding the potential errors inherent in manual operation. Flow-based systems have been developed to provide rapid, low-volume, and high-precision analyses that effectively replace the many tedious and high volume requirements of conventional wet chemistry analyses. This article presents various arrangements of flow-based techniques and their potential use in future enzyme kinetics applications.

Monitoring of chemical and enzymatic hydrolysis of water-soluble proteins using flow-injection analysis with fluorescence detection and an aqueous eluant containing 2-p-toluidinylnaphthalene-6-sulfonate as the fluorescent probe

The exposed hydrophobicity of proteins, which is due to the hydrophobic regions located on their surfaces, enhances the fluorescence intensity of the probe 2-p-toluidinylnaphthalene-6-sulfonate (2,6-TNS) by the formation of a complex. During the hydrolysis of a protein, the average exposed hydrophobicity of the substrate continuously changes with incubation time, and these changes are immediately reflected by a corresponding change in the fluorescence intensity of the 2,6-TNS/substrate complex. Therefore, 2,6-TNS seems to be a good probe to monitor the course of the depolymerization processes of proteins. In this work, bovine serum albumin and alpha-casein have been hydrolyzed both chemically and enzymatically, and the course of the reactions is monitored by using flow-injection analysis (FIA) with fluorescence detection and a buffered aqueous eluant containing 2,6-TNS as the fluorescent probe. Results indicate that the time evolution of the fluorescence intensity of the 2,6-TNS/substrate complex can be correlated with the initial concentration of the parent protein, in mass per unit volume, the hydrolytic activity added, and the time evolution of the mean chain length of the substrate. In addition, because the time elapsed between injection of the sample into the FIA system and measurement of the corresponding fluorescence intensity is only a few seconds, this methodology could be a useful tool for on-line monitoring of processes for the production of protein hydrolysates.

Iteration model of starch hydrolysis by amylolytic enzymes

An elaborate computer program to simulate the process of starch hydrolysis by amylolytic enzymes was been developed. It is based on the Monte Carlo method and iteration kinetic model, which predict productive and non-productive amylase complexes with substrates. It describes both multienzymatic and multisubstrate reactions simulating the "real" concentrations of all components versus the time of the depolymerization reaction the number of substrates, intermediate products, and final products are limited only by computer memory. In this work, it is assumed that the "proper" substrate for amylases is the glucoside linkages in starch molecules. Dynamic changes of substrate during the simulation adequately influence the increase or decrease of reaction velocity, as well as the kinetics of depolymerization. The presented kinetic model, can be adapted to describe most enzymatic degradations of a polymer. This computer program has been tested on experimental data obtained for alpha- and beta-amylases.

Determination of depolymerization kinetics of amylose, amylopectin, and soluble starch by Aspergillus oryzae alpha-amylase using a fluorimetric 2-p-toluidinylnaphthalene-6-sulfonate/flow-injection analysis system

This study reports on the determination of the depolymerization kinetics of amylose, amylopectin, and soluble starch by Aspergillus oryzae alpha-amylase using flow-injection analysis with fluorescence detection and 2-p-toluidinylnaphthalene-6-sulfonate as the fluorescent probe. The experimental data points, corresponding to the evolution of the concentration of "detectable" substrate with depolymerization time, were fit to a single exponential decay curve in the case of amylose and to a double exponential decay curve in the cases of amylopectin and soluble starch. For all the assayed substrates, the determined depolymerization rates at time zero correlated well with the initial enzyme and substrate concentrations through the usual Michaelis-Menten hyperbola. Therefore, this methodology allows the determination of alpha-amylase activity using any of these substrates. For amylopectin and soluble starch, the value of the total depolymerization rate at any depolymerization time was the result of the additive contribution of two partial depolymerization rates. In contrast, the total depolymerization rate for amylose was always a single value. These results, in conjunction with the relative time evolution of the two partial depolymerization rates (for amylopectin and soluble starch), are in good agreement with a linear molecular structure for amylose, a "grape-like" cluster molecular structure for amylopectin, and an extensively degraded grape-like cluster structure for soluble starch.

A monte carlo simulation of the depolymerization of linear homopolymers by endo-enzymes exhibiting random-attack probability and single-attack mechanism: application to the (1-->3), (1-->4)-beta-D-glucan/endo-(1-->3),(1-->4)-beta-D-glucanase system

A Monte Carlo simulation of the depolymerization of linear homopolymers by specific endo-enzymes exhibiting random-attack probability and a single-attack mechanism has been developed. The program simulates the "real" depolymerization versus time of a polydisperse sample of substrate by a specific endo-enzyme. Given the initial mass distribution and concentration of the substrate, the initial concentration of the enzyme, and its Michaelis-Menten constant, the program simulates the evolution of the mass distribution of the substrate with the depolymerization time. When tested against experimental data from the depolymerization of barley (1-->3),(1-->4)-beta-D-glucan by malt endo-(1-->3), (1-->4)-beta-D-glucanase, monitored using the Calcofluor-FIA method with fluorescent detection, excellent results were obtained. Copyright 1998 John Wiley & Sons, Inc.