Polymers biosynthetically prepared

An elegant study of the kinetics has been performed on single-stranded biosynthetic polymers (58), prepared by the method of Bollum et al. (59). Three polymers were used (1) d([3H]pA)B(pA)r2e, (2) d([3H]pA)5(pA)uo ([2- C]pA) - and (3) d([3H]PT)t(PA)in. The digestion was carried out in the presence of Mg2+ and allowed to proceed in a pH stat until 10% of internucleotide bonds were hydrolyzed. The reaction was stopped by heating on a steam bath. The size of the products in the digestion mixture was determined by means of chromatography on a column of Bio-Gel P-60 previously calibrated with oligomers. 

Protein polymers based on Lys-25 were prepared by recombinant DNA (rDNA) technology and bacterial protein expression. The main advantage of this approach is the ability to directly produce high molecular weight polypeptides of exact amino acid sequence with high fidelity as required for this investigation. In contrast to conventional polymer synthesis, protein biosynthesis proceeds with near-absolute control of macromolecular architecture, i.e., size, composition, sequence, topology, and stereochemistry. Biosynthetic polyfa-amino acids) can be considered as model uniform polymers and may possess unique structures and, hence, materials properties, as a consequence of their sequence specificity [11]. Protein biosynthesis affords an opportunity to completely specify the primary structure of the polypeptide repeat and analyze the effect of sequence and structural uniformity on the properties of the protein network. 

Preparation of modified, bacterial polysaccharides having monosaccharide analogs inserted into the polymeric chain is of interest for study of the structure-properties relationship in these biopolymers. Incorporation of chemically prepared, modified, biosynthetic precursors of the polymers in enzymic reactions seems a promising approach for achieving this aim. Such an approach, which may be termed chemical-enzymic synthesis, has now been studied by our group,439-441 using O-specific polysaccharides (10-12) of Salmonella serogroups B and E as an example. 

Only because the remarkable biocompatibility of chemically synthesized poly(GVGVP) was already known was there adequate impetus to purify microbially prepared (GVGVP)2si. Otherwise, it would have been presumed, as had been widely expected, that the toxicity of inadequately purified (GVGVP)25i was an inherent property of the protein-based polymer. To be left in such a state of misunderstanding would have meant that the dramatic potential of elastic protein-based polymers for use in medical applications would be neither appreciated nor realized. The inflammatory response elicited by an inadequately purifled biosynthetic elastic protein-based polymer would have overwhelmed most considered medical applications. 

The mid-chain oxygenated fatty acids that are found in some suberin polymers are generated by the biosynthetic pathways shown in Fig. 6.4.10. Although these pathways have been demonstrated by studies with cell-free preparations of cutin-synthesizing systems, similar reactions are most probably involved in the biosynthesis of suberin monomers. 

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