Biomedical Engineering Reference
In-Depth Information
- carboxypeptidases; hydrolysing peptide bonds at the carboxylic
acid group ends of peptides (-COOH; C-terminal); liberating
single amino acid units. The carboxypeptidase present in
Flavourzyme was cloned, extensively characterized and can be
expressed effi ciently in
Fusarium venenatum
(Blinkovsky et al.
1999).
(2) pH optimum; it is common practice to classify proteases based on their
optimum activity as a function of pH (acid, neutral or alkaline): acid
proteases: pH < 7.0, neutral proteases: pH 7.0 and alkaline proteases:
pH > 7.0.
Fungal acid proteases derived from genera like
Rhizopus
and
Rhizomucor
are applied in dairy applications. Neutral proteases
used in baking products, i.e. for gluten development, are mainly
of the genera
Aspergillus
and
Penicillium
. Most alkaline proteases
are derived from bacilli and used in technical applications, but
also fungal variants (i.e. the Protease P “Amano” 6 produced by
A.
melleus
, Wu et al. 2009) are active at high pH.
(3) proteolytic mechanism; on the basis of the functional group present
at the catalytic site these proteases are classifi ed as serine proteases,
cysteine proteases, aspartic proteases, threonine proteases, glutamic
acid proteases and metalloproteases
Protein hydrolysis
Proteins are high molecular weight, linear polymers of amino acids linked
by peptide bonds. Nature dictates the amino acid sequence in proteins
and the specifi ed location of each amino acid dictates folding of the
polypeptides into three-dimensional structures. Protein structures and
their chemical-physical properties directly impact their susceptibility to
proteolysis. The amino acid composition and sequence of the primary
protein structure infl uences the ease and to what degree varying proteins
can be hydrolyzed by a given protease. Additionally, the spatial structure
of a protein is based on molecular associations that impact protein
solubility and enzyme access to peptide bonds.
Phenomenological properties of proteins in solution are determined
by the intra- and intermolecular forces acting within the system. These
forces (electrostatic, hydrophobic, hydrogen bonding, etc.) determine the
three-dimensional structure of the protein and the physical and chemical
properties, e.g., solubility, foamability, emulsification and gelation.
Proteolysis results in a distortion of intra- and intermolecular interactions
and as a result changes the physical and chemical properties of the system.
The extent of this change depends on the specificity of the protease
