Biosynthesis and Modification of Polymers

Liu JH, Jen HL, Chung YC (1999) Surface modification of polyethylene membrans using phos-phorylcholine derivatives and their platelet compatibility. J Appl Polym Sci 74 2947-2954 Loh SK, ChooYM, Cheng SF, Ma A (2006) Recovery and conversion of palm olein-derived used frying oil to methyl esters for biodiesel. J Oil Palm Res 18 247-252 Loo C-Y, Lee W-H, Tsuge T, Doi Y, Sudesh K (2005) Biosynthesis and characterization of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from pahn oQ products in a Wautersia eutropha mutant. Biotechnol Lett 27 1405-1410... 

A modification of the monosaccharide units of polysaccharides may obviously be effected at different stages of the biosynthesis of a polymer (a) prior to formation of the activated form of a monosaccharide, (b) at the level of glycosyl nucleotides, (c) at the stage of formation of oligosaccharide intermediates, and (d) after the synthesis of a polymeric chain. 

Proteins and peptides are polymers of o-A. a., which are also occur in the free form in all living cells and body fluids. TTie twenty A. a. encoded in messenger RNA (see protein biosynthesis. Genetic code) occur in proteins and are known as proteogenic or proteino-genic A.a. (Table ). The occurrence of nonproteo-genic A. a. in proteins is due to Post-translational modification of proteins (see). Further information on individual A. a. can be found in the appropriate entries. 

We are currently exploring the biosynthesis of novel polyamides from renewable resources using the bacterium Bacillus licheniformis (ATCC 9945a). The use of these polymers for specific biomedical and environmentally degradable polymer applications is currently under investigation. In this paper, we report the effect of culture time and the availability of nutrients on the production and molecular weight of t-PGA. Modification of r-PGA to form water insoluble derivatives will also be described. Finally, characterization of these products by NMR spectroscopy and thermal analysis is reported. 

Genetic modification of the lignin biosynthesis by downregulation of the cinnamoyl-coenzyme A reductase in poplar P. tremula x Populus alba) decreased the lignin content and increased breakdown or remodeling of noncellulosic cell wall polymers as supported by FT-IR analysis [105]. 

It is important to note that the foregoing, biosynthetic-polymer modification is usually incomplete. In fact, only a fraction of the heparin precursor undergoes all of the transformations shown in Scheme 1. However, as the product of each enzymic reaction constitutes the specific substrate for the succeeding enzyme, the biosynthesis of heparin is not a random process. Thus, sulfation occurs preferentially in those regions of the chain where the amino sugar residues have been N-deacetylated and N-sulfated, and where D-glucuronic has been epimerized to L-iduronic acid.20... 

Non-natural amino acids can be incorporated into peptides and polypeptides via several different methodologies. Solid-phase peptide synthesis (SPPS) is a straightforward method for incorporation of non-natural amino acids and allows the incorporation of essentially any amino acid but is limited by the size of the peptides produced 18). Suppression-based strategies, both in vitro and in vivo, have been developed for site specific incorporation of diverse set non-natural amino acids into natural and synthetic polypeptides 19). Alternatively, auxotrophic expression hosts have been used for multisite incorporation of nonnatural amino acid in protein polymers, where multiple natural amino acids of one type can be replaced with non-natural analogues during protein biosynthesis (20, 21). Multisite incorporation of non-natural amino acids in the synthesis of protein polymeric materials facilitates chemical modification at multiple sites and can modulate the physical properties of the protein polymers (22). 

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