261
14
The use of proteins as adhesives and bonding
agents is already mentioned in ancient Hebrew
texts: before the Thanksgiving Day, houses were
painted with casein paints made from curd and
earth pigments. Ancient Egyptian and Chinese
carpenters also used casein glues. Today casein is
used as a building adhesive for carpets, cork and
tiles.
A special challenge for adhesives is bonding under water. However, the common mussel (Mytilus edulis) is able to adhere even in salt
water to various materials such as wood, metals,
stone or plastics. It achieves this with a special
protein that contains l-3,4-dihydroxyphenylalanine (l-DOPA, . Fig. 14.7) as the main component. The two hydroxyl groups of l-DOPA
increase the hydrophilicity of the protein chain
in such a way that the proteinogenic adhesive
achieves a better adhesion effect with the respective substrate under water. This protein cannot be
obtained economically from the mussels. However, it is now also possible to produce these proteins artificially.
The raw materials for the industrial used proteins are usually by-products of plant processing,
e.g. in oil and starch production. For example,
soybeans contain 20% oil and 37% protein. From
the 346 million tons of soybeans harvested in
2018, around 124 million tons of soy protein
are available worldwide - purely mathematically. However, the majority of soy proteins are
currently used for food or animal feed. Animal
proteins such as collagens, gelatine and keratin
are also used industrially. They are explained in
more detail in 7 Sect. 19.2.1 in the description of
biopolymers.
Depending on their structure, proteins can perform various functions in the organism, some of
which have already been mentioned:
5 Structural proteins (keratins, collagen,
fibroin, …),
5 Enzymes (ribonuclease, trypsin, …),
5 Transport proteins (haemoglobin, serum
albumin, myoglobin, …),
5 Storage proteins (ovalbumin, ferritin, …),
5 Hormones (insulin, the “stress hormone”
ACTH, the “growth hormone” somatropin),
5 Protective proteins (blood antibodies, fibrinogen, …),
5 Toxins (snake venoms, botulinus toxin, ricin
castor oil at 7 Sect. 2.2.7, …).
All these proteins - whether with positive properties or highly toxic - consist of the same 20 proteinogenic amino acids presented in 7 Sect. 14.1.
The amino acid sequence and the resulting
structure ultimately determine their biological
activity.
Proteins can also be used in a variety of
industrial applications. Typical fields of application for proteins are:
5 Adhesives, e.g. for the production of chipboards,
5 Paper coatings, e.g. for improved adhesion of
printing inks,
5 Foils, films and coatings, e.g. for the controlled release of active substances,
5 Polymeric materials for applications in horticulture (degradable greenhouse films and
plant pots), food (packaging films), medicine
(absorbable implants) or catering (cutlery,
plates and cups).
14.3 · Proteins
14
The use of proteins as adhesives and bonding
agents is already mentioned in ancient Hebrew
texts: before the Thanksgiving Day, houses were
painted with casein paints made from curd and
earth pigments. Ancient Egyptian and Chinese
carpenters also used casein glues. Today casein is
used as a building adhesive for carpets, cork and
tiles.
A special challenge for adhesives is bonding under water. However, the common mussel (Mytilus edulis) is able to adhere even in salt
water to various materials such as wood, metals,
stone or plastics. It achieves this with a special
protein that contains l-3,4-dihydroxyphenylalanine (l-DOPA, . Fig. 14.7) as the main component. The two hydroxyl groups of l-DOPA
increase the hydrophilicity of the protein chain
in such a way that the proteinogenic adhesive
achieves a better adhesion effect with the respective substrate under water. This protein cannot be
obtained economically from the mussels. However, it is now also possible to produce these proteins artificially.
The raw materials for the industrial used proteins are usually by-products of plant processing,
e.g. in oil and starch production. For example,
soybeans contain 20% oil and 37% protein. From
the 346 million tons of soybeans harvested in
2018, around 124 million tons of soy protein
are available worldwide - purely mathematically. However, the majority of soy proteins are
currently used for food or animal feed. Animal
proteins such as collagens, gelatine and keratin
are also used industrially. They are explained in
more detail in 7 Sect. 19.2.1 in the description of
biopolymers.
Depending on their structure, proteins can perform various functions in the organism, some of
which have already been mentioned:
5 Structural proteins (keratins, collagen,
fibroin, …),
5 Enzymes (ribonuclease, trypsin, …),
5 Transport proteins (haemoglobin, serum
albumin, myoglobin, …),
5 Storage proteins (ovalbumin, ferritin, …),
5 Hormones (insulin, the “stress hormone”
ACTH, the “growth hormone” somatropin),
5 Protective proteins (blood antibodies, fibrinogen, …),
5 Toxins (snake venoms, botulinus toxin, ricin
castor oil at 7 Sect. 2.2.7, …).
All these proteins - whether with positive properties or highly toxic - consist of the same 20 proteinogenic amino acids presented in 7 Sect. 14.1.
The amino acid sequence and the resulting
structure ultimately determine their biological
activity.
Proteins can also be used in a variety of
industrial applications. Typical fields of application for proteins are:
5 Adhesives, e.g. for the production of chipboards,
5 Paper coatings, e.g. for improved adhesion of
printing inks,
5 Foils, films and coatings, e.g. for the controlled release of active substances,
5 Polymeric materials for applications in horticulture (degradable greenhouse films and
plant pots), food (packaging films), medicine
(absorbable implants) or catering (cutlery,
plates and cups).
14.3 · Proteins