Polylysine refers to several types of
lysine homopolymer
A polymer (; Greek '' poly-'', "many" + '' -mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...
s, which may differ from each other in terms of stereochemistry (D/L; the L form is natural and usually assumed) and link position (α/ε). Of these types, only ε-poly-L-lysine is produced naturally.
Chemical structure
The precursor amino acid lysine contains two
amino group
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
s, one at the
α-carbon and one at the ε-carbon. Either can be the location of
polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
, resulting in α-polylysine or ε-polylysine. Polylysine is a homopolypeptide belonging to the group of
cationic
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s: at
pH 7, polylysine contains a positively charged
hydrophilic
A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press.
In contrast, hydrophobes are ...
amino group.
![Alpha-Polylysine](https://upload.wikimedia.org/wikipedia/commons/f/f7/Alpha-Polylysine.png)
α-Polylysine is a synthetic polymer, which can be composed of either
L-lysine or
D-lysine. "L" and "D" refer to the
chirality at lysine's central carbon. This results in poly-
L-lysine (PLL) and poly-
D-lysine (PDL) respectively.
ε-Polylysine (ε-poly-
L-lysine, EPL) is typically produced as a homopolypeptide of approximately 25–30
L-lysine residues.
According to research, ε-polylysine is adsorbed electrostatically to the cell surface of the bacteria, followed by a stripping of the
outer membrane. This eventually leads to the abnormal distribution of the
cytoplasm
In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...
causing damage to the bacterial cell that is produced by bacterial fermentation. ε-Poly-
L-lysine is used as a natural preservative in food products.
Production
Production of polylysine by natural fermentation is only observed in strains of bacteria in the genus ''
Streptomyces''. ''
Streptomyces albulus'' is most often used in scientific studies and is also used for the commercial production of ε-polylysine.
α-Polylysine is synthetically produced by a basic
polycondensation
In polymer chemistry, condensation polymers are any kind of polymers whose process of polymerization involves a condensation reaction (i.e. a small molecule, such as water or methanol, is produced as a byproduct). Condensation polymers are for ...
reaction.
History
The production of ε-polylysine by natural fermentation was first described by researchers Shoji Shima and Heiichi Sakai in 1977.
Since the late 1980s, ε-polylysine has been approved by the Japanese
Ministry of Health, Labour and Welfare
The is a cabinet level ministry of the Japanese government. It is commonly known as in Japan. The ministry provides services on health, labour and welfare.
It was formed with the merger of the former Ministry of Health and Welfare or and the ...
as a preservative in food. In January 2004, ε-polylysine became
generally recognized as safe (GRAS) certified in the United States.
[GRAS Notice No. GRN 000135](_blank)
ε-Polylysine
In food
ε-Polylysine is used commercially as a food
preservative
A preservative is a substance or a chemical that is added to products such as food products, beverages, pharmaceutical drugs, paints, biological samples, cosmetics, wood, and many other products to prevent decomposition by microbial growth or by ...
in Japan, Korea and in imported items sold in the United States. Food products containing polylysine are mainly found in Japan. The use of polylysine is common in food applications such as boiled rice, cooked vegetables, soups,
noodles
Noodles are a type of food made from unleavened dough which is either rolled flat and cut, stretched, or extruded, into long strips or strings. Noodles are a staple food in many cultures (for example, Chinese noodles, Filipino noodles, Ind ...
and sliced fish (
sushi
is a Japanese dish of prepared , usually with some sugar and salt, accompanied by a variety of , such as seafood, often raw, and vegetables. Styles of sushi and its presentation vary widely, but the one key ingredient is "sushi rice," also ...
).
Literature studies have reported an
antimicrobial
An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...
effect of ε-polylysine against
yeast
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
,
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
Gram-positive bacteria and
Gram-negative bacteria
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
.
Polylysine has a light yellow appearance and is slightly bitter in taste whether in powder or liquid form.
α-Polylysine
In tissue culture
α-Polylysine is commonly used to coat tissue cultureware as an attachment factor which improves cell adherence. This phenomenon is based on the interaction between the positively charged polymer and negatively charged cells or proteins. While the poly-
L-lysine (PLL) precursor amino acid occurs naturally, the poly-
D-lysine (PDL) precursor is an artificial product. The latter is therefore thought to be resistant to enzymatic degradation and so may prolong cell adherence.
Polylysine in drug delivery
Polylysine exhibits high positive charge density which allows it to form soluble complexes with negatively charged
macromolecules. Polylysine homopolymers or block copolymers have been widely used for delivery of DNA and proteins. Polylysine-based
nanoparticle
A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 10 ...
s have also been shown to passively accumulate in the injured sites of
blood vessels after
stroke due to incorporation into newly formed
thrombus
A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of ...
, which offers a new way to deliver therapeutic agents specifically to the sites of injury after vascular damage.
Chemical modification
In 2010, hydrophobically modified ε-polylysine was synthesized by reacting EPL with octenyl succinic anhydride (OSA).
[Yu, et al, J. Agri Food Chem, 2010 Jan 27;58(2):1290-5.] It was found that OSA-g-EPLs had glass transition temperatures lower than EPL. They were able to form polymer
micelles
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated coll ...
in water and to lower the surface tension of water, confirming their amphiphilic properties. The antimicrobial activities of OSA-g-EPLs were also examined, and the minimum inhibitory concentrations of OSA-g-EPLs against ''Escherichia coli'' O157:H7 remained the same as that of EPL. Therefore, modified EPLs have the potential of becoming bifunctional molecules, which can be used either as surfactants or emulsifiers in the encapsulation of water-insoluble drugs or as antimicrobial agents.
References
{{reflist
Food additives
Food preservatives
Polymers
Amino acid derivatives