Effect of polyols on fungal alpha-amylase thermostability

Thermal inactivation of a recombinant lipoxygenase from Pseudomonas aeruginosa BBE in the absence and presence of additives

BACKGROUND

Bacterial lipoxygenase (EC 1.13.11.12, LOX) is an important enzyme used as a brightener and strengthening agent during breadmaking. In this study, thermal inactivation of a recombinant LOX of Pseudomonas aeruginosa BBE was characterized by kinetic and thermodynamic analysis in the absence and presence of additives.

RESULTS

As the heating temperature increased from 25 to 55 °C, the thermal inactivation rate (k) values for LOX without the additives ranged from 0.0407 to 0.2627 min(-1), while the half-life (t1/2) values were between 17.08 and 3.25 min. The activation energy (ΔE) values were increased with rise in heating temperatures from 13.26 to 108.9 kJ mol(-1) . Separate tests at 45 °C in the presence of additives (polyols, sugars and ions) at specific concentrations showed that xylitol (1 mol L(-1)) was the most effective stabilizer for recombinant LOX and increased the t1/2 value by 297%.

CONCLUSION

Recombinant LOX was sensitive to heat treatment, and addition of polyols, sugars and ions could enhance its thermal stability. Our findings may provide useful information for stabilizing emerging bacterial LOXs.

Additive effect of dextrans on the stability of horseradish peroxidase

The influence of various concentration (10, 20, and 30% w/v) of different molar weighted dextrans as additives on the stability of HRP has been studied in aqueous medium. Native HRP preparations were formulated with different additives for storage stabilization and better performance at high temperature and pH. The results obtained show a stabilizing effect in the presence of an additive (75 kDa dextran). The enzyme with 75 kDa dextran (in concentration 10% w/v) showed the highest thermal resistance and the best performance for long-term storage at pH 5.0. In the presence of the 75 kDa dextran, the enzyme activity was increased threefold at 25 °C and lost only 15% activity in 2 h at 50 °C in comparison to the native enzyme which lost all its activity. In addition, dextran protected HRP against inactivation by air bubbles.

Mechanism of solvent induced thermal stabilization of papain

In the present study an attempt is made to elucidate the effects of various cosolvents, such as sorbitol, sucrose, xylose and glycerol, on papain. The stabilizing effects of these cosolvents on the structure and function of papain is determined by the activity measurements, fluorescence spectroscopy and differential scanning calorimetry (DSC). The enzyme activity measurements indicate several fold increase in the thermal stability of the enzyme in all the cosolvents used. The thermal denaturation studies of papain in presence of various concentrations of cosolvents indicated a shift in the apparent thermal denaturation temperature (app Tm) suggesting increased thermal stability of papain in presence of cosolvents. The app Tm shifted from a control value of 83+/-1 degrees C to a value of >90+/-1 degrees C in presence of 40% sorbitol. The DSC thermogram for native papain can be clearly deconvoluted into two transitions corresponding to left and right domain and in presence of cosolvents both transitions A and B shift to higher temperature. Maximum stabilization was seen in case of 30% sorbitol where the thermal transition temperatures increased compared to control. The results from partial specific volume measurements of papain in presence of cosolvents suggest that the preferential interaction parameter (xi3) was negative in all cosolvents and maximum hydration was observed in the case of glycerol where the preferential interaction parameter was 0.165g/g. These above results suggest that there is a considerable increase in the thermal stability of papain in presence of these cosolvents as a result of preferential hydration.

An amperometric glucose biosensor prototype fabricated by thermal inkjet printing

The prototype of an amperometric glucose biosensor was realized by thermal inkjet printing using biological and electronic water-based inks, containing a glucose oxidase (GOD) from Aspergillus niger and the conducting polymer blend poly(3,4-ethylenedioxythiophene/polystyrene sulfonic acid) (PEDOT/PSS), respectively. The biosensor was fabricated microdepositing PEDOT/PSS and GOD, in sequence, on ITO-glass, by a commercial inkjet printer, with the help of a commercial software. High density microdots matrices were so-realized, with a calculated resolution of about 221 x 221 dpi (dot per inch). By means of a rapid and easy assay it was demonstrated that no activity loss occurred upon the printing of GOD, despite of the use of a thermal printhead. The device was encapsulated in a semipermeable membrane of cellulose acetate, applied by dip-coating, in order to prevent dissolution of the enzyme and/or PEDOT/PSS in water. The preliminary response of the electrode was measured in an aqueous glucose solution in the presence of ferrocenemethanol (FeMeOH) as a mediator, and resulted linear up to 60 mM in glucose. The best sensitivity value achieved was 6.43 microAM(-1) cm(-2) (447 nAM(-1) U(-1) cm(-2)). The characteristics of the device, and the possible performance improvements have been analyzed and discussed. The reported findings indicate that inkjet printing could be a viable instrument for the easy construction of a working biosensor via direct digital design using biological and conductive polymer based inks. Such an approach may be seen as an example of "biopolytronics".

Stability studies on the cathepsin L proteinase of the helminth parasite, Fasciola hepatica

Fasciola hepatica, the liver fluke, secretes a cathepsin L cysteine proteinase. The enzyme is active over the pH range 5-9 and is remarkably stable at 37 degrees C, pH 7.0, in contrast to mammalian cathepsin Ls that are active in the acidic pH range and are inactivated within 15 min at neutral pH. The liver fluke proteinase is also very tolerant of organic solvents, particularly dimethylformamide. However, it is completely inactivated by 1 mM Hg(2+) and adversely affected by other heavy metals and divalent cations. Addition of glycerol and EDTA enhanced the liver fluke enzyme's stability at 50 degrees C, while glucose and glycerol protected the enzyme from inactivation by repeated freeze-thawing. The high stability of liver fluke cathepsin L suggests that it may have potential for use in bioindustrial applications.

Improved immobilization yields by addition of protecting agents in glutaraldehyde-induced immobilization of protease

The effects of peptides and polyethylene glycol (PEG) on the immobilization of protease using glutaraldehyde-activated Lewatit R258-K resin were investigated. When soy peptide was added at 0.1 g/l, the activity recovery and effectiveness factor increased by 20% and 38%, respectively. When PEG4000 (0.5 g/l) was used as a protecting agent, the activity recovery and effectiveness factor were improved by 35% and 60%, respectively, leading to an increased specific activity of the immobilized enzyme. The addition of PEG4000 is suggested to improve the cost-effectiveness for the production of immobilized enzymes.

Effect of polyols on heat inactivation of Aspergillus niger van Teighem inulinase

The effect of polyols (ethylene glycol, glycerol, erythritol, xylitol and sorbitol) on partially purified inulinase from Aspergillus niger van Teighem mutant grown on Kuth (Saussurea lappa) root as source of inulin was determined. Seventy per cent of inulinase activity was retained in the presence of 4 mol l-1 sorbitol at 75 degrees C.

Amidase activity and thermal stability of human thrombin

Previous studies of amidase activity of human alpha-thrombin have yielded variable results and the decrease of this activity as a function of time and temperature has never been quantified. As this protease is an efficient tool in biochemistry and biotechnology thanks to its extreme selectivity, amidase activity and stability of thrombin were investigated with the synthetic substrate Tos-Gly-Pro-Arg-pNa. Enzyme activity as a function of temperature showed an optimum peak at 45 degrees C. The pH dependence of the activity showed a maximum around 9.5. The addition of NaCl promoted an increase of the activity. Stability of thrombin decreased rapidly when increasing the temperature from 25-45 degrees C and when diluting the enzyme. The presence of glycerol and ethylene glycol promoted a small increase of thrombin half life, whereas polyethylene glycol had a more pronounced positive effect even at very low concentrations.

Effect of polyols on alpha-chymotrypsin thermostability: a mechanistic analysis of the enzyme stabilization

The influence of the synthetic substrate (N-acetyl-L-tyrosine ethyl ester) and the different polyols (ethylene glycol, glycerol, erythritol, xylitol and sorbitol) on the thermostability of alpha-chymotrypsin at 60 degrees C have been studied. The results obtained showed an important stabilizing effect in the presence of both additives. In order to describe the kinetics of enzyme stabilization, the experimental results were analyzed by a four-parameters deactivation model with excellent agreement. In all cases, alpha-chymotrypsin exhibited non-first-order deactivation kinetics, corresponding to a two-step unimolecular mechanism, where the main protective effect of polyols was observed in the first-step of the deactivation profile. Thus, the presence of polyols increased the level of activity stabilization (alpha 1), and decreased the first-order deactivation rate constant (k1). Additionally, the experimental results were analyzed as a function of both, the change in the standard free energy of denaturation (delta(delta Gzero)), and a protective effect, defined as the ratio of alpha-chymotrypsin half-lives (with and without polyols), showing in both cases a clear stabilizing effect of these polyhydroxylic cosolvents for the enzyme. The overall protective effect of polyols was also simultaneously related to their concentration and their water-activity depressing power.

Influence of polyhydroxylic cosolvents on papain thermostability

Papain thermostability was studied, and non-first-order deactivation kinetics were observed. The results obtained were analyzed by a two-step series-type deactivation model involving the native and active enzyme, an active intermediate enzyme state, and a final inactive state, with excellent agreement. The influence of different polyhydroxylic cosolvents (ethylene glycol, glycerol, erythritol, xylitol and sorbitol) on the thermostability of papain at 60 degrees C was also studied. Analysis of the results by the assayed model showed that the main protective effect of cosolvents was observed in the second step of the deactivation profile. The results obtained were analyzed as a function of both the thermodynamic parameters and a protective effect, defined as the ratio of papain half-lives (with and without cosolvents) for the second deactivation step, showing in both cases an important stabilizing effect of these cosolvents on the enzyme. The overall protective effect of cosolvents was also related simultaneously to their concentration and their water activity-depressing power.