J.P. Dubes

Bio: J.P. Dubes is an academic researcher from University of Provence. The author has contributed to research in topics: Aqueous solution & Critical micelle concentration. The author has an hindex of 15, co-authored 38 publications receiving 634 citations.

Distinction between esterases and lipases: a kinetic study with vinyl esters and TAG.

Abstract: The better to characterize enzymes hydrolyzing carboxyl ester bonds (carboxyl ester hydrolases), we have compared the kinetic behavior of various lipases and esterases against solutions and emulsions of vinyl esters and TAG. Short-chain vinyl esters are hydrolyzed at comparable rates by esterases and lipases and have higher limits of solubility in water than corresponding TAG. Therefore, they are suited to study the influence of the physical state of the substrate on carboxyl ester hydrolase activity within a large concentration range. Enzymes used in this study are TAG lipases from microorganisms, lipases from human and guinea pig pancreas, pig liver esterase, and acetylcholinesterase. This study also includes cutinase, a fungal enzyme that displays functional properties between esterases and lipases. Esterases display maximal activity against solutions of short-chain vinyl esters (vinyl acetate, vinyl propionate, and vinyl butyrate) and TAG (triacetin, tripropionin, and tributyrin). Half-maximal activity is reached at ester concentrations far below the solubility limit. The transition from solution to emulsion at substrate concentrations exceeding the solubility limit has no effect on esterase activity. Lipases are active on solutions of short-chain vinyl esters and TAG but, in contrast to esterases, they all display maximal activity against emulsified substrates and half-maximal activity is reached at substrate concentrations near the solubility limit of the esters. The kinetics of hydrolysis of soluble substrates by lipases are either hyperbolic or deviate from the Michaelis-Menten model and show no or weak interfacial activation. The presence of molecular aggregates in solutions of short-chain substrates, as evidenced by a spectral dye method, likely accounts for the activity of lipases against soluble esters. Unlike esterases, lipases hydrolyze emulsions of water-insoluble medium- and long-chain vinyl esters and TAG such as vinyl laurate, trioctanoin, and olive oil. In conclusion, comparisons of the kinetic behavior of carboxyl ester hydrolases against solutions and emulsions of vinyl esters and TAG allows the distinction between lipases and esterases. In this respect, it clearly appears that guinea pig pancreatic lipase and cutinase are unambiguously classified as lipases.

1H and 13C NMR studies of the self-association of chlorpromazine hydrochloride in aqueous solution

Abstract: The 1H NMR spectrum of chlorpromazine hydrochloride was fully assigned at 400 MHz. Similarly, the 13C NMR spectrum was assigned unambiguously using two-dimensional NMR. Measurements of chemical shift as a function of concentration in D2O showed appreciable changes of shift of both protons and carbons which were apparent even at solution concentrations two orders of magnitude lower than the critical micelle concentration (CMC). The relative magnitude of the shifts of the aromatic protons and carbons on dilution below the CMC were compatible with vertical stacking of the molecules in an off-set manner such that maximum overlap of the chlorinated rings occurred. Proton chemical shift data were interpreted using a stepwise association model to quantify the extent of association in the pre-CMC region.

A calorimetric study on the self-association of an amphiphilic phenothiazine drug in aqueous electrolyte solutions

Abstract: The association characteristics of an amphiphilic phenothiazine drug, promethazine hydrochloride, in aqueous solutions containing high concentrations of electrolyte have been examined by heat conduction calorimetry. The application of deconvolution techniques has permitted the continuous determination of the concentration dependence of the apparent molar enthalpy extending to regions of high dilution. Theoretical treatments have been derived to describe thermogenesis in solutions of amphiphilic compounds exhibiting a range of association patterns. The calorimetric data for promethazine hydrochloride in the presence of 0.2-0.6 mol dm -3 sodium chloride could be satisfactorily described by an association scheme in which a primary unit of 3-4 monomers is formed below the critical micelle concentration by a continuous self-association process and grows with increasing concentration by the stepwise addition of monomers

A calorimetric study of the influence of electrolyte on the micellisation of phenothiazine drugs in aqueous solution

Abstract: Apparent molar enthalpies have been determined as a function of concentration by heat conduction calorimetry for aqueous solutions of the phenothiazine drugs chlorpromazine hydrochloride, promethazine hydrochloride, and promazine hydrochloride in the presence of added electrolyte (0.025−0.10 mol dm-3 NaCl). The concentration dependence of the apparent molar enthalpy could be quantitatively described using a mass action model of association based on the Guggenheim equations for the activity coefficients for mixed electrolytes. Derived values of the monomer−counterion interaction coefficient became increasingly negative with increase of salt concentration, suggesting that electrolyte addition promoted association at concentrations below the critical micelle concentration (cmc). Calculations of the fraction of each drug in the form of micelles as a function of concentration further confirmed the tendency for premicellar association. Significant differences in properties were observed between promethazine and...

Optimization of extracellular lipase production by Geotrichum sp. using factorial design.

Abstract: Response surface methodology was employed to study the effects of carbon source (soy oil, olive oil and glucose) and nitrogen source concentrations (corn steep liquor and NH(4)NO(3)) on the lipase production by Geotrichum sp. The experiment included a 2(4) central composite rotatable design (CCRD) and four others 2(3) CCRD. According to the responses from the experimental designs, the effects of each variable were calculated and the interactions between them were determined. The response surface methodology was applied for the optimization of the nutrient concentrations in the culture medium for the enzyme production, at 30 degrees C. The optimum medium composition for lipase production by Geotrichum sp. was ammonium nitrate 2.1-2.5%, corn steep liquor 13-15% and soy oil 0.6% as carbon source, which lead to a lipase activity of about 20 U/ml. Using olive oil as carbon source, the optimum composition was ammonium nitrate 0.8-1%, corn steep liquor 13-15% and olive oil 0.6%, leading to an activity of 17 U/ml.

Lipases: an overview.

Abstract: Lipases are ubiquitous enzymes, widespread in nature. They were first isolated from bacteria in the early nineteenth century, and the associated research continuously increased due to the characteristics of these enzymes. This chapter reviews the main sources, structural properties, and industrial applications of these highly studied enzymes.

Solvent as electron donor: Donor/acceptor electronic coupling is a dynamical variable

Abstract: We combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken−Hush (GMH) theory in the study of electron-transfer reactions and electro...

Identification and characterization of a new true lipase isolated through metagenomic approach

Abstract: Metagenomics, the application of molecular genomics to consortia of non-cultivated microbes, has the potential to have a substantial impact on the search for novel industrial enzymes such as esterases (carboxyl ester hydrolases, EC 3.1.1.1) and lipases (triacylglycerol lipases, EC 3.1.1.3). In the current work, a novel lipase gene was identified from a fosmid metagenomic library constructed with the "prokaryotic-enriched" DNA from a fat-contaminated soil collected from a wastewater treatment plant. In preliminary screening on agar containing 1% tributyrin, 2661 of the approximately 500,000 clones in the metagenomic library showed activity. Of these, 127 showed activity on agar containing 1% tricaprylin, while 32 were shown to be true lipase producers through screening on agar containing 1% triolein. The clone with the largest halo was further characterized. Its lipase gene showed 72% identity to a putative lipase of Yersinia enterocolitica subsp. palearctica Y11. The lipase, named LipC12, belongs to family I.1 of bacterial lipases, has a chaperone-independent folding, does not possess disulfide bridges and is calcium ion dependent. It is stable from pH 6 to 11 and has activity from pH 4.5 to 10, with higher activities at alkaline pH values. LipC12 is stable up to 3.7 M NaCl and from 20 to 50°C, with maximum activity at 30°C over a 1 h incubation. The pure enzyme has specific activities of 1722 U/mg and 1767 U/mg against olive oil and pig fat, respectively. Moreover, it is highly stable in organic solvents at 15% and 30% (v/v). The combination of the use of a fat-contaminated soil, enrichment of prokaryotic DNA and a three-step screening strategy led to a high number of lipase-producing clones in the metagenomic library. The most notable properties of the new lipase that was isolated and characterized were a high specific activity against long chain triacylglycerols, activity and stability over a wide range of pH values, good thermal stability and stability in water-miscible organic solvents and at high salt concentrations. These characteristics suggest that this lipase has potential to perform well in biocatalytic processes, such as for hydrolysis and synthesis reactions involving long-chain triacylglycerols and fatty acid esters.