Insoluble Polyesters

Since poly(hydroxybutyrate), a naturally abundant poly(hydroxyalkanoate) (PHA, Fig. 1), was first isolated and characterized by Lemoigne in 1925, PHAs have been studied extensively by biochemists who referred to them as lipids [1, 2]. Further research on PHAs however, made it clear that these materials are in fact water-insoluble polyesters, which are synthesized and accumulated intra-cellularly as storage compounds by many different bacteria. Using various types of substrates, an almost infinite variety of PHAs can be synthesized [3-9]. 

The aliphatic components of SOM, derived from various sources, tend to persist in soil (Almendros et al. 1998 Lichtfouse et al. 1998a Lichtfouse et al. 1998b Mosle et al. 1999 Poirier et al. 2000). The principal source of aliphatic materials in soil is plant cuticular materials, especially cutin, an insoluble polyester of cross-linked hydroxy-fatty acids and hydroxy epoxy-fatty acids (Kolattukudy 2001). Some plant cuticles also contain an acid and base hydrolysis-resistant biopolymer, comprised of aliphatic chains attached to aromatic cores known as cutan (Tegelaar et al. 1989 McKinney et al. 1996 Chefetz 2003 Sachleben et al. 2004). 

A radiometric and a spectrometric assay have been developed to measure PhaC activity. The radiometric assay measures the incorporation of isotope-labeled hydroxyacyl moieties into the polyester, which is present from the beginning as primer [17]. [3-14]ft-(-)-3-hydroxybutyryl-CoA or [3H]-P,S-3-hydroxybutyryl-CoA or in principle any other CoA thioester of a radioactively-labeled hydroxyacyl moiety could be used as substrate. Only the radioactivity that is really incorporated into the insoluble polyester is measured. The time course of the assay, the need to synthesize the substrates and the high costs make the assay very inconvenient and it is hardly used anymore. A more convenient assay is the spectrometric assay which measures the release of coenzyme A during the polymerization reaction in presence of Ellmann s reagent 5,5 -dithiobis-(2-nitrobenzoic acid) (DTNB) yielding 5 -thio(2-nitrobenzoate) that absorbs at about 412 nm [16], Here, the enzyme activity is measured directly without delay. However, it is not the formation of the polymeric product that is measured, but the release of coenzyme A, which can also be due to the hydrolytic cleavage of the substrate by another enzyme that does not have any PhaC activity, like a thioesterase. Nevertheless, this assay is now most frequently used due to its convenience. 

Two other synthetic materials quickly followed. Dacron, a useflil high-melting and insoluble polyester, was developed by the British chemists Rex Whinfield and James T. Dickson and marketed in Britain by Imperial Chemical Industries as Terylene. In Germany chemists of the I. G. Farben developed polyurethane foams, and in the United States Roy J. Plunkett, a Du Pont chemist, 2 years beyond his Ph.D., discovered Teflon when he opened a gas cylinder supposed to contain a fluorinated hydrocarbon but nothing came out. He became curious, and after inserting a wire through the valve to make sure the tank was indeed open, he cut the tank in half and found a waxy white powder in the bottom. He tested the properties of the material, found it was inert to acids, bases, heat, and solvents, and very slippery. 

Bitton G (1980) Adsorption of viruses to surfaces technological and ecological implications. In Bitton G, Marshall KC (eds) Adsorption of microorganisms to surfaces. Wiley, New York, pp 331—374 Bitton G (1994) Processes based on attached microbial growth. In Bitton G (ed) Wastewater microbiology. Wiley, New York, pp 189-198 Blake RC II, Norton WN, Howard GT (1998) Adherence and growth of a Bacillus species on an insoluble polyester polyurethane. Int Biodeter Biodegr 42 63-73... 

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