Enzymes are formed in all living
organisms where they catalyze and regulate essential chemical reactions needed
for the life of organism (Nisha and Divakaran, 2014).
Enzymes are proteins in nature. They
are fragile and large molecules. Hence enzymes are completely different from the
well-known organic and inorganic catalysts. Soluble enzymes are regarded as being
instable and sensitive to process conditions (Biro et al., 2008; Buchholz
et al., 2012).
Enzymes as biocatalysts
Enzymes are biocatalysts which have different
applications in industrial chemistry (Wohlgemuth, 2010). This
application includes purified enzymes, immobilized enzymes or immobilized cells
as catalysts for the process mentioned above (Schmid et al., 2001; Gong et al.,
2012). The development of biocatalysts is completely targeted to the
progress of protein expression, metabolic engineering, large-scale genome
sequencing and detected evolution (Bornscheuer et al., 2012).
Biocatalysts have a critical importance for
processes of industrial, pharmaceutical and biotechnological application (Sanchez
and Demain, 2010). The success of enzyme application for any enzymatic
processes depends on the cost competitiveness as well as the well-established
chemical methods (Tufvesson et al.,
When being compared to chemical
catalysts, it is noted that enzymes are more incline to be consequently and are
used in performing molecular transformations which cannot be achievable by ordinary
chemical catalysis (Liese et al.,
Enzymes which are thermostable at high
temperatures are more desirable in industrial applications. The rate of
reaction typically increases every 10°C increase in temperature thus most
enzymes do not withstand high temperatures over higher than 40°C and they can
be denatured at extreme values of pH (Cornish-Bowden, 2004).
When applied to the industrial
biocatalysts area, enzymes are proven to provide a great success. Various
factors may affect the application of biocatalysts, such factors are enzyme
promiscuity, screening technologies as well as robust computational methods for
improving the properties of enzyme available for the applications (Adrio and
In fact, the biotechnological
processes have many advantages over well-established chemical processes such as
having less catalyst waste, increased catalyst efficiency as well as a lower
energy demand. They might be around 150 biocatalytic processes that are being
applied in industry (Panke and Wubbolts, 2005). However, the new
development in protein engineering made it easier to successfully use
particular enzyme characteristics in industrial purpose (Lutz, 2010).
According to the fact that enzymes
are involved in all aspects of biochemical conversion varying from the simple
enzyme or fermentation conversion leading to the complex techniques in genetic
engineering, it is fair to say that enzymes are considered as a focal point of
biotechnological processes (Ebbs, 2004).
Environmental and genetic manipulations
can be used to increase the enzyme levels. Thousand-fold increases have been observed
for catabolic enzymes, and biosynthetic enzymes have been increased several
hundred-fold (Burns and Dick, 2002).
Many disadvantages have been noted in
the processes of different industries such as the production of pharmaceuticals
and chemicals. These disadvantages may include the need for high temperature, low
catalytic efficiency, low pH and high pressure. Not to mention that using
organic solvents produces pollutants and organic waste. Enzymes like
biocatalysts are more useful for the applications mentioned above because they have
a long half-life, work under slight reaction conditions and they work on abnormal
substrates (Johnson, 2013).
In addition to this, enzymes can be selected
genetically or chemically-modified in order to be used for improving some
characteristics like stability, substrate specificity and specific activity.
However, some disadvantages are found in enzymes including the requirement of
certain co-factor by enzymes. There are different ways that can be used in
order to solve such a problem among which using the whole cells as well as
recycling of cofactor (Baici, 2015).
Reports show that enzymes isolated
from microbes are applied in pharmaceuticals as diagnostic reagents, as
reagents for the production of chemicals, food additives, the manufacture of
detergents, the treatment of industrial wastes and bioremediation (Baxter
and Cummings, 2006).
Stability of enzyme
Stability of enzymes is an important
concern especially during thermal processing. Losing enzyme activity at high
temperature ranges is directly related to variations of enzyme conformation (Cui
et al., 2008, Fu et al., 2010). One can estimate this through thermodynamic
parameters and Arrhenius equation (Marangoni, 2003).
In a nutshell, enzyme stability is absolutely
essential in basic and applied enzymology. Enzyme stabilization principles
could only be understood through illustrating how enzymes lose their activity
followed by deriving the structure stability relationships existing in
enzymatic molecules (Plou et al.,
The most important outcome of using
enzymes is to produce useful compounds. Since the fact that enzymes are
unstable and can be quickly inactivated through different mechanisms, they
cannot be the proper catalysts for industrial applications. Having a stable
enzyme in soluble form is inevitable to achieve the storage of purified enzymes
and the purification processes as well (Aehle, 2007).
Different strategies have been used in
order to enhance enzyme stability. The well-known methods for obtaining soluble
stable enzymes are: 1) chemical modifications of enzymes and 2) use of
additives (Taravati et al., 2007, Shelley, 2011).
Additives are soluble compounds that
have a particular effect on the thermostability of the enzyme protein. Remarkable
effect on the enzyme stability is noticed when particular compounds to enzyme
solutions are added. Such additives are polymers, polyhydrilic, sugar,
alcohols, and other organic solvents (Polaina and Maccabe, 2007).
certain types of chemicals could be used in avoiding such conformational
changes of the enzyme. These chemicals include polyols which is mainly used to
promote numerous hydrogen bonds or salt-bridge formation between amino acid
residues. These bonds or bridges make the enzyme molecule more rigid, hence it
becomes more resistant to the thermal unfolding (George et al., 2001; Costa et al.,
2002). However, the choosing of the appropriate additive depends on the