Enzymes are formed in all livingorganisms where they catalyze and regulate essential chemical reactions neededfor the life of organism (Nisha and Divakaran, 2014).
Enzymes are proteins in nature. Theyare fragile and large molecules. Hence enzymes are completely different from thewell-known organic and inorganic catalysts. Soluble enzymes are regarded as beinginstable and sensitive to process conditions (Biro et al., 2008; Buchholzet al., 2012).
Enzymes as biocatalystsEnzymes are biocatalysts which have differentapplications in industrial chemistry (Wohlgemuth, 2010). Thisapplication includes purified enzymes, immobilized enzymes or immobilized cellsas catalysts for the process mentioned above (Schmid et al., 2001; Gong et al.,2012). The development of biocatalysts is completely targeted to theprogress of protein expression, metabolic engineering, large-scale genomesequencing and detected evolution (Bornscheuer et al.
, 2012). Biocatalysts have a critical importance forprocesses of industrial, pharmaceutical and biotechnological application (Sanchezand Demain, 2010). The success of enzyme application for any enzymaticprocesses depends on the cost competitiveness as well as the well-establishedchemical methods (Tufvesson et al.
,2010).When being compared to chemicalcatalysts, it is noted that enzymes are more incline to be consequently and areused in performing molecular transformations which cannot be achievable by ordinarychemical catalysis (Liese et al.,2006).Enzymes which are thermostable at hightemperatures are more desirable in industrial applications.
The rate ofreaction typically increases every 10°C increase in temperature thus mostenzymes do not withstand high temperatures over higher than 40°C and they canbe denatured at extreme values of pH (Cornish-Bowden, 2004).When applied to the industrialbiocatalysts area, enzymes are proven to provide a great success. Variousfactors may affect the application of biocatalysts, such factors are enzymepromiscuity, screening technologies as well as robust computational methods forimproving the properties of enzyme available for the applications (Adrio anddemain, 2014).In fact, the biotechnologicalprocesses have many advantages over well-established chemical processes such ashaving less catalyst waste, increased catalyst efficiency as well as a lowerenergy demand. They might be around 150 biocatalytic processes that are beingapplied in industry (Panke and Wubbolts, 2005).
However, the newdevelopment in protein engineering made it easier to successfully useparticular enzyme characteristics in industrial purpose (Lutz, 2010).According to the fact that enzymesare involved in all aspects of biochemical conversion varying from the simpleenzyme or fermentation conversion leading to the complex techniques in geneticengineering, it is fair to say that enzymes are considered as a focal point ofbiotechnological processes (Ebbs, 2004).Environmental and genetic manipulationscan be used to increase the enzyme levels.
Thousand-fold increases have been observedfor catabolic enzymes, and biosynthetic enzymes have been increased severalhundred-fold (Burns and Dick, 2002).Many disadvantages have been noted inthe processes of different industries such as the production of pharmaceuticalsand chemicals. These disadvantages may include the need for high temperature, lowcatalytic efficiency, low pH and high pressure. Not to mention that usingorganic solvents produces pollutants and organic waste. Enzymes likebiocatalysts are more useful for the applications mentioned above because they havea long half-life, work under slight reaction conditions and they work on abnormalsubstrates (Johnson, 2013).In addition to this, enzymes can be selectedgenetically or chemically-modified in order to be used for improving somecharacteristics like stability, substrate specificity and specific activity.However, some disadvantages are found in enzymes including the requirement ofcertain co-factor by enzymes.
There are different ways that can be used inorder to solve such a problem among which using the whole cells as well asrecycling of cofactor (Baici, 2015).Reports show that enzymes isolatedfrom microbes are applied in pharmaceuticals as diagnostic reagents, asreagents for the production of chemicals, food additives, the manufacture ofdetergents, the treatment of industrial wastes and bioremediation (Baxterand Cummings, 2006).Stability of enzymeStability of enzymes is an importantconcern especially during thermal processing.
Losing enzyme activity at hightemperature ranges is directly related to variations of enzyme conformation (Cuiet al., 2008, Fu et al., 2010). One can estimate this through thermodynamicparameters and Arrhenius equation (Marangoni, 2003).In a nutshell, enzyme stability is absolutelyessential in basic and applied enzymology. Enzyme stabilization principlescould only be understood through illustrating how enzymes lose their activityfollowed by deriving the structure stability relationships existing inenzymatic molecules (Plou et al.
,2009).The most important outcome of usingenzymes is to produce useful compounds. Since the fact that enzymes areunstable and can be quickly inactivated through different mechanisms, theycannot be the proper catalysts for industrial applications.
Having a stableenzyme in soluble form is inevitable to achieve the storage of purified enzymesand the purification processes as well (Aehle, 2007).Different strategies have been used inorder to enhance enzyme stability. The well-known methods for obtaining solublestable enzymes are: 1) chemical modifications of enzymes and 2) use ofadditives (Taravati et al., 2007, Shelley, 2011).Additives are soluble compounds thathave a particular effect on the thermostability of the enzyme protein. Remarkableeffect on the enzyme stability is noticed when particular compounds to enzymesolutions are added. Such additives are polymers, polyhydrilic, sugar,alcohols, and other organic solvents (Polaina and Maccabe, 2007).
Addingcertain types of chemicals could be used in avoiding such conformationalchanges of the enzyme. These chemicals include polyols which is mainly used topromote numerous hydrogen bonds or salt-bridge formation between amino acidresidues. These bonds or bridges make the enzyme molecule more rigid, hence itbecomes more resistant to the thermal unfolding (George et al., 2001; Costa et al.,2002).
However, the choosing of the appropriate additive depends on theenzyme structure.