Stabilization of a raw starch digesting amylase from Aspergillus carbonarius via immobilization on activated and non-activated agarose gel

Graphene oxide/chitosan composites as novel support to provide high yield and stable formulations of pectinase for industrial applications

An extracellular pectinase from a mixed consortium of Bacillus sp. (BSP) was immobilized onto graphene oxide/chitosan composite (GO/CS) through covalent binding to enhance its recycling and operational stability features. Different parameters were optimized, including cross-linker concentration (%), time, pH, and GO/CS-pectinase ratios. GO/CS-pectinase was further characterized by FT-IR and XRD. The activity of GO/CS-pectinase was reached up to 804 μmolmin^-1 with an immobilization efficiency of 80.64 ± 1.15 % under optimum conditions. GO/CS-pectinase exhibited a 3.0-folds higher half-life (t_1/2) than free pectinase at 50, 55, and 60 °C, respectively. The V_max and K_M values of GO/CS-pectinase were found to be nearly equal to the free pectinase indicating that conformational flexibility was retained. K_d, t_1/2, ∆G*, ∆H*, and ∆S* of both free pectinase and GO/CS-pectinase was 0.0339 & 0.0721 min^-1, 9.62 and 40.44 min, 81.35, 90.72 kJmol^-1, 47.098 & 63.635 kJmol^-1, -102.86 & -81.340 Jmole^-1 K^-1. SEM morphological analysis further confirmed the successful binding of pectinase with GO/CS, which retained about 92 % of its original catalytic activity after ten consecutive reaction cycles. Finally, GO/CS-pectinase was employed for guava juice clarification which exhibited the turbidity reduction up to 81 % after 75 min of treatment.

Efficient secretion expression of phospholipase D in Bacillus subtilis and its application in synthesis of phosphatidylserine by enzyme immobilization

Transphosphatidylation catalyzed by phospholipase D has gained increasing attention for producing phosphatidylserine (PS), which can be used in functional food and medicine. In this study, we investigated the effects of six signal peptides on the secretion of PLD (PLD_sa) from Streptomyces antibioticus TCCC 21059 in the food-grade GRAS bacterium Bacillus subtilis. It indicated that the optimal signal peptide DacB with an Ala-X-Ala sequence motif at the C-terminus showed the highest secretory expression ability, resulting in increased production of 2.84 U/mL PLD_sa. Then PLD_sa was immobilized on the epoxy-based carriers, and one of these carriers allowed PLD_sa loading of up to 2.7 mg/g. The immobilized PLD_sa was more stable over a wide range of pH value (4.5-7.5) and temperature (16 °C-60 °C) than free PLD_sa. Subsequently, the synthesis of PS from soybean phosphatidylcholine (PC) was carried out in purely aqueous solution using immobilized PLD_sa, leading to a high yield of 65%. The immobilized PLD_sa catalyst maintained a relative PS production of 60% after 5 recycles. Notably, the use of toxic solvent was completely eliminated in the whole process, which would be more profitable for the application of PS.

Citraconylation and maleylation on the catalytic and thermodynamic properties of raw starch saccharifying amylase from Aspergillus carbonarius

Amylase capable of raw starch digestion presents a cheap and easier means of reducing sugar generation from various starch sources. Unfortunately, its potential for use in numerous industrial processes is hindered by poor stability. In this work, chemical modification by acylation using citraconic anhydride (CA) and maleic anhydride (MA) was used to stabilize the raw starch saccharifying amylase from A. carbonarius. The effect of the anhydrides on the pH and thermal stability of the free amylase was investigated. Enzyme kinetics and thermodynamic studies of the free and modified amylase were also carried out. Blue shifts in fluorescent spectra were observed after modification with both anhydrides. Citraconylation led to increased affinity of the enzyme for raw potato starch, unlike maleylation. The activation energy (kJ mol⁻¹) for enzyme inactivation was increased by 94.8% after modification with CA while only 17.9% increase was noted after modification with MA. Acylation led to an increase in Gibb's free energy and enthalpy while a reduction in entropy was observed. At 80 °C the half-life (h) was 5.92, 11.18 and 14.74 for free, MA and CA enzyme samples, respectively. These findings have potential value in all industries interested in starch conversion to sugars.

From protein engineering to immobilization: promising strategies for the upgrade of industrial enzymes

Enzymes found in nature have been exploited in industry due to their inherent catalytic properties in complex chemical processes under mild experimental and environmental conditions. The desired industrial goal is often difficult to achieve using the native form of the enzyme. Recent developments in protein engineering have revolutionized the development of commercially available enzymes into better industrial catalysts. Protein engineering aims at modifying the sequence of a protein, and hence its structure, to create enzymes with improved functional properties such as stability, specific activity, inhibition by reaction products, and selectivity towards non-natural substrates. Soluble enzymes are often immobilized onto solid insoluble supports to be reused in continuous processes and to facilitate the economical recovery of the enzyme after the reaction without any significant loss to its biochemical properties. Immobilization confers considerable stability towards temperature variations and organic solvents. Multipoint and multisubunit covalent attachments of enzymes on appropriately functionalized supports via linkers provide rigidity to the immobilized enzyme structure, ultimately resulting in improved enzyme stability. Protein engineering and immobilization techniques are sequential and compatible approaches for the improvement of enzyme properties. The present review highlights and summarizes various studies that have aimed to improve the biochemical properties of industrially significant enzymes.