Activity and Conformation of Yeast Alcohol Dehydrogenase (YADH) Entrapped in Reverse Micelles

Protein thermal stability in the undergraduate biochemistry laboratory: Exploring protein thermal stability with yeast alcohol dehydrogenase

We created a novel laboratory experience where undergraduate students explore the techniques used to study protein misfolding, unfolding, and aggregation. Despite the importance of protein misfolding and aggregation diseases, protein unfolding is not typically explored in undergraduate biochemistry laboratory classes. Yeast alcohol dehydrogenase (YADH) is used in the undergraduate biochemistry laboratory course at Miami University as the model system to explore protein overexpression and purification, bioinformatics, and enzyme characterization. Using one model protein across the entire semester allows the students to independently link topics introduced in the individual experiments; for example, students might draw connections between the thermal denaturation experiment and the requirement to keep the enzyme cold during a kinetics experiment. Students quantitated changes in secondary structure resulting from thermal denaturation by analyzing circular dichroism data. Monitoring the turbidity of a YADH solution with a temperature-controlled UV-Vis spectrometer was a reliable and easy method for undergraduate students to observe the thermally-induced aggregation of YADH. Together these experiments provide undergraduate students with first-hand experience in techniques to study protein unfolding and aggregation.

How the external solvent in biocompatible reverse micelles can improve the alkaline phosphatase behavior

In the last decade, the nature of the nonpolar solvents that can be part of reverse micelles (RMs) has been the topic of several investigations to improve their applications. In this sense, the hydrolysis of 1-naphthyl phosphate catalyzed by the enzyme alkaline phosphatase (AP) was used as a probe to investigate the effect of the change of the external solvent on RMs formulated with the anionic surfactant sodium diethylhexyl sulfosuccinate (AOT). As external nonpolar solvents, two biocompatible lipophilic esters, isopropyl myristate and methyl laurate, and the traditional nonpolar solvents, n-heptane and benzene, were used. The results were compared among the RMs investigated and with the reaction in homogeneous media. Thus, the effect of the nanoconfinement as well as the impact of the replacement of a conventional external nonpolar solvent by biocompatible solvents were analyzed. The results indicate that the catalytic efficiency in the AOT RMs is larger than that in homogeneous media, denoting a different hydration level over the AP enzyme, which is directly related to the different degrees of nonpolar solvent penetration to the RM interface. Our findings demonstrated that toxic solvents such as n-heptane and benzene can be replaced by nontoxic ones (isopropyl myristate or methyl laurate) in AOT RMs without affecting the performance of micellar systems as nanoreactors, making them a green and promising alternative toward efficient and sustainable chemistry.

A novel water-in-ionic liquid microemulsion and its interfacial effect on the activity of laccase

It is of great significance to develop an appropriate water-in-ionic liquid (W/IL) microemulsion suitable for the expression of the catalytic activity of a given enzyme. In this paper, the phase diagram of a new AOT/Triton X-100/H(2)O/[Bmim][PF(6)] pseudo ternary system is presented. With the aid of nonionic surfactant Triton X-100, AOT could be dissolved in hydrophobic ionic liquid [Bmim][PF(6)], forming a large single phase microemulsion region. The water-in-[Bmim][PF(6)] (W/IL) microemulsion domain was identified electrochemically by using K(3)Fe(CN)(6) as a probe. The existence of W/IL microemulsions was demonstrated spectrophotometrically by using CoCl(2) as a probe. New evidences from the FTIR spectroscopic study, which was first introduced to the W/IL microemulsion by substituting D(2)O for H(2)O to eliminate the spectral interference, demonstrated that there existed bulk water at larger ω(0) values (ω(0) was defined as the molar ratio of water to the total surfactant) in the W/IL microemulsion, which had remained unclear before. In addition to the inorganic salts, biomacromolecule laccase could be solubilized in the W/IL microemulsion. The laccase hosted in the microemulsion exhibited a catalytic activity and the activity could be regulated by the composition of the interfacial membrane.

Activity and kinetics studies of yeast alcohol dehydrogenase in a reverse micelle formulated from functional surfactants

Yeast alcohol dehydrogenase (YADH) showed substantial decrease in its catalytic activity due to the strong electrostatic interaction between the head groups of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and YADH in AOT reverse micelles. However, the catalytic activity of YADH in a nonionic reverse micellar interface (GGDE/TX-100) obtained from a functional nonionic surfactant N-gluconyl glutamic acid didecyl ester (GGDE) and Triton X-100 (TX-100) was higher than that in AOT reverse micelle under the respective optimum conditions. A comparison of the kinetic parameters showed that the turnover number kcat in GGDE/TX-100 reverse micelle was 1.4 times as large as that in AOT reverse micelle, but the Michaelis constants in AOT reverse micelle for ethanol K mB was twice and for coenzyme NAD+ K mA was 5 times higher than their counterparts in GGDE/TX-100 reverse micelle. For the conversion of ethanol, the smaller K mB and larger kcat in GGDE/TX-100 reverse micelle resulted in higher catalytic efficiency kcat/K mB. The stability of YADH in GGDE/TX-100 reverse micelle was also found to be better than that in AOT reverse micelle. They were mainly attributed to the absence of electric charge on the head groups of GGDE and TX-100 in the GGDE/TX-100 reverse micelle.

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

The effect of surfactants, both in water-in-oil microemulsions (hydrated reverse micelles) and aqueous solutions upon enzymatic processes is reviewed, with special emphasis on the effect of the surfactant upon the kinetic parameters of the process. Differences and similarities between processes taking place in aqueous and organic solvents are highlighted, and the main models currently employed to interpret the results are briefly discussed.

Kinetics of N-glutaryl-L-phenylalanine p-nitroanilide hydrolysis catalyzed by α-chymotrypsin in aqueous solutions of dodecyltrimethylammonium bromide

The rate of hydrolysis of N-glutaryl-L-phenylalanine p-nitroanilide (GPNA) catalyzed by alpha-chymotrypsin (alpha-CT) has been measured in aqueous solutions of dodecyltrimethylammonium bromide (DTAB) at concentrations below and above the critical micelle concentration, as well as in the absence of surfactant. Under all the conditions employed, the reaction follows a Michaelis-Menten mechanism. The presence of the surfactant leads to superactivity below and above the critical micelle concentration (CMC), with a maximum reaction rate taking place near the CMC when the results are treated in terms of the analytical concentration of the substrate. A similar behavior was observed by working with the enzyme partially deactivated in the presence of 4 M urea. After correction to take into account the partitioning of the substrate between the micelles and the external media, the activity of the enzyme tends to remain almost constant above the corresponding CMCs. This results from a compensation of a decrease in the catalytic constant (k(cat)) and a decrease in the Michaelis constant (K(M)). The behavior of alpha-CT in the hydrolysis of GPNA in DTAB solutions is at variance with that previously reported for the hydrolysis of 2-naphthyl acetate in solutions of the same surfactant (E. Abuin, E. Lissi, R. Duarte, Langmuir 19 (2003) 5374). An explanation of the different effects of the surfactant on the behavior of the enzyme with both substrates is advanced, taking into account the complexity of the mechanism of the alpha-CT-mediated reaction, more specifically, in terms of different rate-limiting steps for the formation of the measured products.

Effect of the addition of a nonaqueous polar solvent (glycerol) on enzymatic catalysis in reverse micelles. Hydrolysis of 2-naphthyl acetate by alpha-chymotrypsin

The kinetics of hydrolysis of 2-naphthyl acetate (2-NA) catalyzed by alpha-chymotrypsin (alpha-CT), in reverse micellar solutions formed by glycerol (GY)-water (38% v/v) mixture/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-heptane has been determined by spectroscopic measurements. To compare the efficiency of this reaction with that observed in micelles with water in the core, as well as in the corresponding homogeneous media, the reaction was also studied in water/AOT/n-heptane reverse micellar solutions and in both homogeneous media (water and GY-water, 38% v/v mixture). In every media, alpha-CT was characterized by the absorption and emission spectra, the fluorescence lifetimes, and the fluorescence anisotropy of its tryptophan residues. The effect of AOT concentration on the kinetic parameters obtained in the micellar systems was determined, at a constant molar ratio of the inner polar solvent and surfactant. Moreover, the data obtained allowed the evaluation of the 2-NA partition constant between the organic and the micellar pseudophase. It is shown that the addition of GY to the micelle interior results in an increase in the catalytic properties of alpha-CT. The fluorescence anisotropy studies in the different media show that the addition of GY increases the viscosity as compared with the aqueous systems. It seems that the GY addition to the reverse micellar aggregates results in a decrease of the conformational mobility of alpha-CT, which leads to an increase of the enzyme stability and activity.