Enzyme polymer modification

DNA is ideally suited as a structural material in supramolecular chemistry. It has sticky ends and simple rules of assembly, arbitrary sequences can be obtained, and there is a profusion of enzymes for modification. The molecule is stiff and stable and encodes information. Chapter 10 surveys its varied applications in nanobiotechnology. The emphasis of Chapter 11 is on DNA nanoensembles, condensed by polymer interactions and electrostatic forces for gene transfer. Chapter 12 focuses on proteins as building blocks for nanostructures. 

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... 

Keywords MonolithPorous polymer, Separation, HPLC, Capillary electrochromatography, Enzyme immobilization, Modification... 

In the area of enzymatic polymer synthesis, one can distinguish between enzymatic polymerization and enzymatic polymer modification. Of the six main enzyme groups (see Table 3.3), three have been used as catalysts for enzymatic polymerization and four have been used in enzymatic polymer modification reactions. 

Another field of enzymatic polymer synthesis is the enzyme-catalyzed modification of preformed polymers by esterification or transesterification. Thereby, it is possible to either introduce functional side groups into an existing polymer with a stable backbone (no polyester) to synthesize functional homopolymers as well as random copolymers or to generate multiblock copolymers by enzymatic transesterification between two different homopolymers. 

Polymer Modification by Oxidoreductases. Tyrosinase (polyphenol oxidase, a copper-containing monooxygenation enzyme) was used as catalyst for modification of chitosan. The enzymatic treatment of chitosan film in the presence of tyrosinase and phenol derivatives produced a new material of chitosan derivative (309). During the reaction, imstable o-quinones were formed, followed by the reaction with chitosan to give the modified chitosan. In the enzymatic treatment of p-cresol with a low concentration of chitosan (<1%), the reaction solution was converted into a gel (310). 

Gtibitz GM, Cavaco-Paulo A (2003) New substrates for reliable enzymes enzymatic modification of polymers. Curr Opin Biotech 14 577-582... 

Duxbury and coworkers recently developed a new chiral enzyme-responsive polymer based on enantioselective polymer modification [151]. With the aid of two alcohol dehydrogenases that show opposite enantioselectivities in the reduction of ketones (ADH-LB and ADH-T), the two enantiomers of p-vinylpheny-lethanol were obtained in excellent yield and ee. Copolymers of these monomers with styrene using free radical polymerization afforded random block copolymers... 

Fig. 20 Schematic illustration of regioselective polymer modification a Pendant group is too short to form the acyl enzyme intermediate in the active site (illustrated by the serine OH group), b When the pendant group is longer the acyl-enzyme intermediate is formed (a), and the transesterification occurred (b) to give the product (c) [152]. Reproduced by permission of the American Chemical Society (ACS)...

After over fifteen years of intense research PHCs have passed from a short list of raw materials to a lai e number of variously functionalized polymers. Modification of the monomeric structures has allowed processability by conventional polymer techniques and the specificity for applications such as fine tuning of color for displays or enzyme recognition. Conductive properties have been greatly improved so that conductivities as high as 5000 S cm have been obtained [434] while for the optoelectronic characteristics the... 

This overview briefly surveys the use of enzymatic and wholecell approaches in polymers. Three types of reactions are covered polymer syntheses, polymer modifications, and polymer hydrolyses. Thus far, most of the enz3une-related R D activities involve hydrolases, oxidoreductases, and transferases, with occasional use of lyases and isomerases. Whole-cell methods continue to be valuable in both academic and industrial labs. All these research areas display continued vitality and creativity, as evidenced by the large number of publications. Advances in biotechnology have provided new and improved enzymes and additional tools. Also included in diis overview is the related topic of biomaterials. 

Enzymes are conunonly classified, via a system of Enzyme Commission (EC) numbers, into six divisions oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases (34). In this work, we are concerned with three types of polymer reactions polymer syntheses, polymer modifications, and polymer degradation and hydrolyses. For these reactions, only hydrolases, oxidoreductases, and transferases are being used extensively in polymers and biomaterials. A summary is given in Table 1. 

Enzyme-Catalyzed Condensation Reactions for Polymer Modifications... 

That this is in fact an equilibrium process is proven by the observation that the same equilibrium copolymer is obtained either from PCMT or from P3CT. We anticipate extension of this chemistry to polymers other than polysulfides, as well as applications in adhesives, in polymer modification and in enzyme immobilization. 

Kruus K., Niku-Paavola, M.L. and Viikari L.(2001) Laccase-a Useful Enzyme for Modification of Biopolymers, In Biorelated Polymers-Sustainable Polymer Science and Technology, E. Chiellini, H. Gil, G. Braunegg, J. Buchert, P. Gatenholm, and M. Van der Zee (eds.), Kluwer Academic/Plenum Publishers, pp.255-261... 

Following the epimerization step, three different O-sulfation reactions take place, starting with 2-0 sulfation of IdoA residues and followed by 6-0 sulfation and 3-0 sulfation of GlcN units. While several isoforms with different substrate specificities have been found both for the 6-0- and the 3-0-sulfotransferases (see the main text), only one mammalian 2-0-sulfotransferase has so far been identified (45). This enzyme species appears to catalyze also 2-O-sulfation of GlcA units, a less common reaction. The precise relation of this latter step to the other polymer-modification reactions is unclear. 

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