Poly extracellular

Galactosylated chitosan prepared from lactobionic acid and chitosan with l-ethyl-3-(3-dimethylaminopropyl)-carbodiimideand N-hydroxysuccinimide was a good extracellular matrix for hepatocyte attachment [155] (Fig. 4). Furthermore, graft copolymers of galactosylated chitosan with poly(ethylene glycol) or poly(vinyl pyrrolidone) were useful for hepatocyte-targeting DNA carrier [156,157]. 

Mutans streptococci are the major pathogenic organisms of dental caries in humans. The pathogenicity is closely related to production of extracellular, water-insoluble glucans from sucrose by glucosyltransferase and acid release from various fermentable sugars. Poly(catechin) obtained by HRP catalyst in a phosphate buffer (pH 6) markedly inhibited glucosyltransferase from Streptococcus sorbrinus 6715, whereas the inhibitory effect of catechin for this enzyme was very low. 

Collmer A, Batemann DF (1982) Regulation of extracellular pectate lyase in Erwinia chrysanthemi. evidence that reaction products of pectate lyase and exo-poly-a-D-galacturonase mediate induction on galacturonan. Physiol Plant Pathol 21 127-139... 

An extracellular enzyme from Xanthomonas sp. is able to degrade poly(c -l,4-isoprene) with the production of 12-keto-4,8-dimethyltrideca-4,8-diene-l-al (Braaz et al. 2004), and functions as a heme-dependent oxygenase (Braaz et al. 2005). 

Dextran is the collective name of extracellular bacterial poly-alpha-D-glucopyranoses linked largely by 1,6 bonds, with branching occurring at the 1,2, 1,3 or 1,4 bonds. Physical properties vary... 

Synthetic Polymers. Synthetic polymers are versatile and offer promise for both targeting and extracellular-intracellular drug delivery. Of the many soluble synthetic polymers known, the poly(amino acids) [poly(L-lysine), poly(L-aspartic acid), and poly(glutamic acid)], poly(hydroxypropylmethacrylamide) copolymers (polyHPMA), and maleic anhydride copolymers have been investigated extensively, particularly in the treatment of cancers. A brief discussion of these materials is presented. 

Polyesters, such as microbially produced poly[(P)-3-hydroxybutyric acid] [poly(3HB)], other poly[(P)-hydroxyalkanoic acids] [poly(HA)] and related biosynthetic or chemosynthetic polyesters are a class of polymers that have potential applications as thermoplastic elastomers. In contrast to poly(ethylene) and similar polymers with saturated, non-functionalized carbon backbones, poly(HA) can be biodegraded to water, methane, and/or carbon dioxide. This review provides an overview of the microbiology, biochemistry and molecular biology of poly(HA) biodegradation. In particular, the properties of extracellular and intracellular poly(HA) hydrolyzing enzymes [poly(HA) depolymerases] are described. 

Extracellular Degradation of Polymers Related to Bacterial Poly(HA) 316... 

Identification and Isolation of Extracellular Poly(HA)-Degrading Microorganisms... 

The ability to degrade extracellular poly(HA) is widely distributed among bacteria and fungi and depends on the secretion or surface-display of specific... 

Extracellular, exo-type poly(/3-L-malic acid) hydrolase 124... 

Brandi et al. [71] using culture fluid of Acidovorax delafieldii and cyclic 3HB oligomers were in agreement with the presence of endo-hydrolase activity of poly(3HB) depolymerases. Similar results were obtained by de Koning et al. [72] who demonstrated that covalently cross-linked poly(HAMCL) was hydrolyzed completely by P. fluorescens. It is assumed that most - if not all - extracellular poly(HA) depolymerases have endo- and exo-hydrolase activity. Depending on the depolymerase the hydrolysis products are only monomers, monomers and dimers, or a mixture of oligomers (mono- to trimers). 

The i-poly(3HB) depolymerase of R. rubrum is the only i-poly(3HB) depolymerase that has been purified [174]. The enzyme consists of one polypeptide of 30-32 kDa and has a pH and temperature optimum of pH 9 and 55 °C, respectively. A specific activity of 4 mmol released 3-hydroxybutyrate/min x mg protein was determined (at 45 °C). The purified enzyme was inactive with denatured poly(3HB) and had no lipase-, protease-, or esterase activity with p-nitro-phenyl fatty acid esters (2-8 carbon atoms). Native poly(3HO) granules were not hydrolyzed by i-poly(3HB) depolymerase, indicating a high substrate specificity similar to extracellular poly(3HB) depolymerases. Recently, the DNA sequence of the i-poly(3HB) depolymerase of R. eutropha was published (AB07612). Surprisingly, the DNA-deduced amino acid sequence (47.3 kDa) did not contain a lipase box fingerprint. A more detailed investigation of the structure and function of bacterial i-poly(HA) depolymerases will be necessary in future. 

A different pH-triggered deshielding concept with hydrophilic polymers is based on reversing noncovalent electrostatic bonds [78, 195, 197]. For example, a pH-responsive sulfonamide/PEl system was developed for tumor-specific pDNA delivery [195]. At pH 7.4, the pH-sensitive diblock copolymer, poly(methacryloyl sulfadimethoxine) (PSD)-hZocA -PEG (PSD-b-PEG), binds to DNA/PEI polyplexes and shields against cell interaction. At pH 6.6 (such as in a hypoxic extracellular tumor environment or in endosomes), PSD-b-PEG becomes uncharged due to sulfonamide protonation and detaches from the nanoparticles, permitting PEI to interact with cells. In this fashion PSD-b-PEG is able to discern the small difference in pH between normal and tumor tissues. 

Figure 4.10. Dose-relationships for histamine release from rat mast cells induced by a variety of peptides [99], No calcium was added to the extracellular medium. Each point is the mean of two or more determinations A, poly(L-lysine) (molecular weight 30.000-70,000) , succinylated poly(L-lysine) (molecular weight 30,000-70f)00) V, [n-Phe7 )SP , fD-Prcr2, D-Phe7, D-Trpv]SP, u , SP/ A, eledoisin-related peptide , eledoisin O, N-terminal tetrapeptide of substance P.

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