Protease Proteases
(Proteinases, Peptidases or Proteolytic enzymes) are enzymes that break
peptide bonds between amino acids of proteins. The process is called proteolytic
cleavage, a common mechanism of activation or inactivation of enzymes especially
involved in blood coagulation or digestion. They use a molecule of water for this
and are thus classified as hydrolases.
There are
currently six classes of proteases:
- Serine
proteases
- Threonine
proteases
- Cysteine
proteases
- Aspartic
acid proteases (e. g. plasmepsin)
- Metalloproteases
- Glutamic
acid proteases
Occurrence:
Proteases
occur naturally in all organisms and constitute 1-5% of the gene content. These
enzymes are involved in a multitude of physiological reactions from simple digestion
of food proteins to highly regulated cascades (e.g. the blood clotting cascade,
the complement system, apoptosis pathways, and the invertebrate prophenoloxidase
activating cascade). Peptidases can break either specific peptide bonds (limited
proteolysis), depending on the amino acid sequence of a protein, or break down
a complete peptide to amino acids (unlimited proteolysis). The activity can be
a destructive change abolishing a protein's function or digesting it to its principal
components, it can be an activation of a function or it can be a signal in a signalling
pathway.
Protease split peptide bonds with water ,they attack proteins via
two modes,yielding different end products.Therefore ,your choice of enzyme may
be dictated by what you require as hydrolysis product. On
there mode of attack proteases are classified into two: - Exoprotease:
These
are proteases which can cleave off single amino acids from either end of the protein
chain.Eventually under right conditions a protein can be reduced down to a single
amino acids.
-
Endoproteases:
These are proteases which attack
peptide bonds on the interior of the protein chain.The hydrolysis products are
usually smaller polypeptides and peptides. Therefore most endoproteins will not
produce a great deal of free amino acids as end products.
Specificity:
Threre are many different protease, each with a different specificity toward protein
substrates. Applications:
- Protease
is a commercially important enzyme, it has a wide industrial application some
of which are
- The
greatest industrial use of protease is for laundry detergents where they help
to remove protein based stains (such as blood and egg) from clothing.
- The
second largest use of protease is for cheese making. Enzymes from calf stomach
and microbial sources are used to clot milk-one of the first steps in cheesemaking.
- Proteases
are also used for bating(softening) leather, modifying food ingredients(e.g. soy
protein whipping agents),meat tenderizers, and flavor development
- Proteases
have also been studied for their role in blood clotting and inflammatory diseases.
Classification:
Proteases
have been classified on different criteria it can be on the bases of their sources,
biochemical activity, and pH. On basis of pH Proteases are classified as: - Acid
Protease:These are proteases that show maximum activity at acidic PH.
- Microbial
Rennets: Higly specific endoproteases used to clot milk in cheese making.
Source:
Mucor miehei.M. pusillus, Endothia parasitica - Renin:
Highly specific endoprotease used to clot milk in cheesemaking
Source: Calf
stomach - Pepsin:
An endoprotease that will hydrolyze a broad range of synthetic peptides. Commercial
products have exoprotease and esterase side activities.Pepsin prefers to cleave
bonds near phenylalanine and leucine residues.
Source: Swine and bovine stomach - Fungal
Acid Proteases: Hydrolyzes a wide range of peptide bonds. Preparations usually
exhibit endo- and exo- protease activity.
Source: Molds- Aspergillus, Rhizopus - Neutral
Protease: These are proteases that show maximum activity at Neutral pH.
- Trypsin:
Highly specific endoprotease which prefers to cleave bonds next to arginine and
lysine residues.
Sources:Bovine and swine pancrease glands - Papain:Endoprotease
that hydrolyzes a wide range of peptide bonds. It is a sulfhydryl protease requiring
mild reducing agents.
Souces: Papaya latex - Bromelain/Ficin:
Endoprotease that hydrolyze a wide range of peptide bonds and are similar to papain.
Usually sold as a mixture of proteases.
Source: Pineapple and fig respectively - Bacterial
Neutral Protease:An endoprotease that hydrolyses a wide range of peptide bonds.
Source:
Bacillus subtilis - Alkaline
Protease:These are proteases that show maximum activity at Alkaline pH.
- Subtilisin
(and related protease): An endoprotease that hydrolyze a wide range of peptide
bond preferences.
Source: Bacillus subtilis and others in this gene
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