Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
2001-08-17
2002-12-17
Acquah, Samuel A. (Department: 1711)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C528S361000, C528S364000, C528S373000, C528S374000, C435S130000, C435S131000, C435S135000, C435S136000, C435S141000, C435S146000, C514S512000, C514S712000
Reexamination Certificate
active
06495152
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally in the field of biopolymers, and in particular describes a class of polythioesters which can be produced by bacterial fermentation.
Polymers are the most abundant molecules in living matter. There are seven general classes of biopolymers are distinguished: polynucleotides, polyamides, polysaccharides, polyisoprenes, lignin, polyphosphate and polyhydroxyalkanoates, PHA (Müller & Seebach, 1993) (Table 1). Poly(3-hydroxybutyrate), PHB, belongs to the latter class as a wide spread bacterial storage compound and was already observed in 1926 as hydrophobic inclusions in the cytoplasm of
Bacillus megaterium
(Lemoigne, 1926). Today many genera of bacteria are known to accumulate PHAs as energy and carbon source mostly under restricted growth conditions, e.g. oxygen- or nitrogen-limitation (Anderson & Dawes, 1990; Steinbüchel, 1991).
Polyhydroxyalkanoates (PHAs) are polymers with repeating hydroxy acid monomeric units. PHAs have been reviewed in several publications, including Byrom, “Miscellaneous Biomaterials,” in
Biomaterials
(D. Byrom, ed.) pp. 333-59 (MacMillan Publishers, London 1991); Hocking and Marchessault, “Biopolyesters” in
Chemistry and Technology of Biodegradable Polymers
(G. J. L. Griffin, ed.) pp. 48-96 (Chapman and Hall, London 1994); Müller and Seebach,
Angew. Chem. Int. Ed. Engl
., 32:477-502 (1993); Steinbüchel, “Polyhydroxyalkanoic Acids,” in
Biomaterials
(D. Byrom, ed.) pp. 123-213 (MacMillan Publishers, London 1991); and Williams and Peoples,
CHEMTECH
, 26:38-44 (1996).
TABLE 1
Eight classes of biopolymers and characteristics of their
biosynthesis and occurrence
Template-dependent
Substrate of the
Synthesis in
Class
synthesis
polymerase
Prokaryote
Eukaryote
Nucleic acids
yes
DNTPs, NTPs
yes
yes
Proteins and
yes
aminoacyl-tRNAs
yes
yes
Polyaminoacids
no
amino acids
yes
yes
Polysaccharides
no
Sugar-NDP, Sucrose
yes
yes
Polyhydroxyalkanoate
no
Hydroxyacyl Co A
yes
no
Polythiesters
no
Mercaptoacyl Co A
yes
no
Polyphosphate
no
ATP
yes
yes
Polyisoprenoids
no
A*
no
only plants
Lignin
no
B*
no
only plants
*A: Isopentenylpyrophosphate;
B: Radicalic intermediates.
A wide range of bacteria are known to accumulate polyhydroxyalkanoates (PHA) as intracellular storage compounds. Due to the properties of these polymers as biodegradable thermoplastics, and elastomers they have attracted much interest and are considered for various technical applications in industry, medicine, agriculture and other areas (Anderson, A. J. & Dawes, E. A.,
Microbiol. Rev
. 54, 450-472 (1990); Steinbüchel, 1991).
Several types of polyhydroxyalkanoates are formed in nature by various organisms in response to environmental stress. These PHAs can be broadly divided into three groups according to the length of their pendant groups and their respective biosynthetic pathways. Relatively short pendant groups include the C
3-5
hydroxy acids, whereas relatively long pendant groups include C
6-14
hydroxy acids.
There are three major types of naturally occurring PHAs. The first type includes only relatively short hydroxy acid monomeric units. The second type include both relatively short and relatively long hydroxy acid monomeric units. The third type includes only relatively long hydroxy acid monomeric units. Those with short pendant groups, such as polyhydroxybutyrate (PHB), a homopolymer of R-3-hydroxybutyric acid (R-3HB) units, are highly crystalline thermoplastic materials (Lemoigne and Roukhelman,
Annales des fermentations
, 5:527-36 (1925)). PHAs containing the short R-3HB units randomly polymerized with much longer pendant group hydroxy acid units were first reported in the early seventies (Wallen and Rohwedder,
Environ. Sci. Technol
., 8:576-79 (1974)). A number of microorganisms which specifically produce copolymers of R-3HB with these longer pendant group hydroxy acid units are also known and belong to this second group (Steinbüchel and Wiese,
Appl. Microbiol Biotechnol
., 37:691-97 (1992)). In the early 1980's, a research group in The Netherlands identified the third group of PHAs, which contains predominantly longer pendant group hydroxy acids (De Smet, et al.,
J. Bacteriol
., 154:870-78 (1983)).
PHAs may constitute up to 90% of the dry cell weight of bacteria, and are found as discrete granules inside the bacterial cells. These PHA granules accumulate in response to nutrient limitation and serve as carbon and energy reserve materials. Distinct pathways are used by microorganisms to produce each group of these polymers. One of these pathways leading to the short pendant group polyhydroxyalkanoates (SPGPHAs) involves three enzymes: thiolase, reductase, and PHB synthase (sometimes called polymerase). Using this pathway, the homopolymer PHB is synthesized by condensation of two molecules of acetyl-Coenzyme A to give acetoacetyl-Coenzyme A, followed by reduction of this intermediate to R-3-hydroxybutyryl-Coenzyme A, and subsequent polymerization. The last enzyme in this pathway, the synthase, has a substrate specificity that can accommodate C
3-5
monomeric units, including R-4-hydroxy acid and R-5-hydroxy acid units. This biosynthetic pathway is found, for example, in the bacteria
Zoogloea ramigera
and
Alcaligenes eutrophus.
The biosynthetic pathway which is used to make the third group of PHAs, long pendant group polyhydroxyalkanoates (LPGPHAs), is still partly unknown. However, it is currently thought that the monomeric hydroxyacyl units leading to the LPGPHAs are derived by the &agr;-oxidation of fatty acids and the fatty acid pathway. The R-3-hydroxyacyl-Coenzyme substrates resulting from these routes are then polymerized by PHA synthases (sometimes called polymerases) that have substrate specificities favoring the larger monomeric units in the C
6-14
range. LPGPHAs are produced, for example, by Pseudomonads.
The second group of PHAs containing both short R-3HB units and longer pendant group monomers are believed to utilize both the pathways to provide the hydroxy acid monomers. The latter are then polymerized by PHA synthases able to accept these units.
Roughly 100 different types of PHAs have been produced by fermentation methods so far (Steinbüchel and Valentin,
FEMS Microbiol., Lett
., 128:219-28 (1995)). A number of these PHAs contain functionalized pendant groups such as esters, double bonds, alkoxy, aromatic, halogens, and hydroxy groups. Transgenic systems for producing PHAs in both microorganism and plants, as well as enzymatic methods for PHA synthesis, are reviewed by Williams and Peoples,
CHEMTECH
, 26:38-44 (1996).
Two PHAs belonging to the first group, polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHBV), have been extensively studied. PHBV is a copolymer of R-3HB units with 5-24% R-3-hydroxyvaleric acid (R-3HV), and is known commercially as Biopol™ (supplied by ICI/Zeneca). These polymers are natural thermoplastics which can be processed using conventional polymer technology and which have industrially useful properties, such as biodegradability in soil and marine environments and good barrier properties. They are characterized by melting points which range from 130 to 180° C., and extensions-to-break of 8 to 42% (see Zeneca Promotional Literature, Billingham, UK 1993).
So far, more than 130 different hydroxyalkanoic acids have been described as constituents of PHAs, comprising 3-, 4-, 5-, and 6-hydroxyalkanoic acids of various chain length. The pendant alkyl side chain can in addition contain various constituents (for review see Steinbüchel & Valentin, 1995). Whereas the large variety of PHA constituents refers almost exclusively to the modified side chains in the &bgr;-position of the hydroxyalkanoic acids, PHAs with modified backbones are rare. Examples are 2-methyl-3-hydroxybutyric acid and 3-hydroxypivalic acid, which have been identified as PHA constituents resulting in polymer chains with one or two methyl groups, respectively, in the backbone (Satho et al., (1992)
Wat. Sci. Technol
. 26, 933-942; Füchtenbusch et al., (1998)
FEMS Microbiol. Lett
. 159, 85-92).
Bact
Ewering Christian
Lütke-Eversloh Tina
Steinbuchel Alexander
Acquah Samuel A.
Holland & Knight LLP
Tepha, Inc.
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