[20, 21]. Breakdown of peptide bonds helps in the protein degradation into their
constituent amino acids, smaller peptides or it can be specific, leads to selective
protein cleavage for post-translational modification (PTM) and processing [22].
Proteases are categorized as peptidases or peptide hydrolases (EC 3.4) and comprise
a large family of enzymes, divided into endopeptidases (EC 3.4.21–99) and exopeptidases (EC 3.4.11–19) and grouped depending on the position of the peptide bond
to be cleaved. Protease can also be classified according to the pH range where they
have optimal activity: acidic (pH 2.0–6.0), neutral (pH 6.0–8.0) and alkaline
(pH 8.0–13.0) [13, 23, 24].
The growing realization of a diverse array of biological, economic and technical
challenges has generated renewed interest in the study of proteolytic enzymes for
different industrial applications. The most common proteases of animal origin include
pepsin, pancreatic, rennins, trypsin and chymotrypsin. Plant origin proteases consist
of papain, bromelain and keratinases. Use of plant proteases is controlled by land
availability for agriculture, labour, government policies and climate, while the recovery of animal protease in bulk is determined by the presence of livestock for slaughter,
which in turn is dictated by environmental, political, religious belief and government
policies. The failure of plant and animal protease to quench market demands has led to
an increased interest in microbial proteases [25]. Microbial sources of protease are
widely preferred for industrial application because of the following advantages:
• Require limited space for their production.
• Broad biochemical diversity.
• Rapid growth of the microorganisms and faster production.
• Flexibility in production.
• Ease of genetic manipulation to generate enzymes for different characteristics and
applications.
• The enzyme can be easily recovered.
• Microorganisms can secrete large amount of enzymes for large-scale applications.
• Economical.
Microbial proteases are derived from a wide variety of microorganisms, which
include bacteria, yeasts and fungi. Proteases of industrial value are mainly obtained
from microorganisms, and these are Bacillus species from the bacterial kingdom and
Aspergillus from the fungal kingdom because they are known to be generally
recognized as safe (GRAS) [26]. Proteases have been used in laundry and detergent
industries for over 50 years to facilitate release of proteinaceous materials in stains
and account for about 25% of total worldwide sales of enzymes [27]. Detergent
industry heavily uses thermostable alkaline proteases from thermophiles as an
additive [28]. Other enzymes used in detergents include amylases, mannanase,
cellulase and lipases. The use of different enzymes as detergent additives arises
from the fact that proteases can hydrolyse proteinaceous stains, cellulases are
effective in cleaning, colour clarification and anti-redeposition (cotton), mannanases
are perfect for stain removal, amylases are effective against starch and other carbohydrate stains, while lipases are effective against oily or fat stains [29, 30]. An ideal
enzyme for detergent should have broad substrate specificity, be stable at high pH
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
203
constituent amino acids, smaller peptides or it can be specific, leads to selective
protein cleavage for post-translational modification (PTM) and processing [22].
Proteases are categorized as peptidases or peptide hydrolases (EC 3.4) and comprise
a large family of enzymes, divided into endopeptidases (EC 3.4.21–99) and exopeptidases (EC 3.4.11–19) and grouped depending on the position of the peptide bond
to be cleaved. Protease can also be classified according to the pH range where they
have optimal activity: acidic (pH 2.0–6.0), neutral (pH 6.0–8.0) and alkaline
(pH 8.0–13.0) [13, 23, 24].
The growing realization of a diverse array of biological, economic and technical
challenges has generated renewed interest in the study of proteolytic enzymes for
different industrial applications. The most common proteases of animal origin include
pepsin, pancreatic, rennins, trypsin and chymotrypsin. Plant origin proteases consist
of papain, bromelain and keratinases. Use of plant proteases is controlled by land
availability for agriculture, labour, government policies and climate, while the recovery of animal protease in bulk is determined by the presence of livestock for slaughter,
which in turn is dictated by environmental, political, religious belief and government
policies. The failure of plant and animal protease to quench market demands has led to
an increased interest in microbial proteases [25]. Microbial sources of protease are
widely preferred for industrial application because of the following advantages:
• Require limited space for their production.
• Broad biochemical diversity.
• Rapid growth of the microorganisms and faster production.
• Flexibility in production.
• Ease of genetic manipulation to generate enzymes for different characteristics and
applications.
• The enzyme can be easily recovered.
• Microorganisms can secrete large amount of enzymes for large-scale applications.
• Economical.
Microbial proteases are derived from a wide variety of microorganisms, which
include bacteria, yeasts and fungi. Proteases of industrial value are mainly obtained
from microorganisms, and these are Bacillus species from the bacterial kingdom and
Aspergillus from the fungal kingdom because they are known to be generally
recognized as safe (GRAS) [26]. Proteases have been used in laundry and detergent
industries for over 50 years to facilitate release of proteinaceous materials in stains
and account for about 25% of total worldwide sales of enzymes [27]. Detergent
industry heavily uses thermostable alkaline proteases from thermophiles as an
additive [28]. Other enzymes used in detergents include amylases, mannanase,
cellulase and lipases. The use of different enzymes as detergent additives arises
from the fact that proteases can hydrolyse proteinaceous stains, cellulases are
effective in cleaning, colour clarification and anti-redeposition (cotton), mannanases
are perfect for stain removal, amylases are effective against starch and other carbohydrate stains, while lipases are effective against oily or fat stains [29, 30]. An ideal
enzyme for detergent should have broad substrate specificity, be stable at high pH
Alkaliphilic Enzymes and Their Application in Novel Leather Processing. . .
203