Intracellular storage polymers

PHB is a material that features outstanding properties among thermoplastics by being embedded into nature s closed cycles. The polyester can be produced from renewable raw materials such as sucrose from sugarcane via microbial cultivations in bioreactors. For their biosynthesis, several microbial strains are of interest. These organisms accumulate PHA as intracellular storage compounds. After extraction and purification of the polymer, it can be processed into desired products and... 

Since a wide variety of bacteria are accumulating PHAs as intracellular storage material this natural polymer is considered as a potential substitute for petrochemical plastics (24). Medium chain length t es are semicrystalline elastomers with a low melting point. 

The kinetics of urinary excretion of PVP of various molecular weights was found to be biphasic In the first (steeper) phase, the excreted fraction represents mainly the polymer filtered directly from the plasma. The second, slower phase probably reflects the transport of the polymer from other compartments, i.e. interstitial fluid, lymph etc., to the plasma compartment. The rate of this transport is also dependent on the molecular size Mainly the high molecular weight fractions can remain in the interstitial fluid for a sufficiently long time to be captured by cells via pinocyto-sis. Intracellular storage of polymers in secondary lysosomes represents the only demonstrated mode of polymer deposition in the body for a period of time ranging from months to years. 

Stanier, Wilkinson, and their co-workers (Macrae, 1958 Stanier, 1959 Williamson, 1958) have evenly reported that PHA acted as an intracellular food and eneigy reserve in bacteria. The polymer is prodnced by the cell in response to a nutrient limitation in the enviromnent in order to prevent starvation in the case where an essential element is nnavailable. The nntrient hmitation activates a metabolic pathway activating the PHA prodnction PHA represented as caibon-storage polymers. 

Polyhydroxyalkanoates (PHAs), also known as microbial polyesters , or bacterial plastics are biosynthetic, biocomapatible, and biodegradable thermoplastics. They are bacterial storage polymers produced by various microorganisms (e.g., A.eutrophus, P.oleovorans, R.rubrum, Rb.spaeroides) in response to nutrient limitation occuring in the presence of an excess of carbon (see Chapters 9 and 10), and function as intracellular reserves of carbon and energy as well as ion sinks. 

Polymers of fructose are of widespread occurrence in plants, but are common only in a few orders, particularly the Compositae ind Graminae, They differ in several respects from prokaryotic fructans, especially in that they are intracellular rather than extracellular, that they are far smaller than their bacterial counterparts and that they contain relatively more glucose. Their function in plants is as storage polysaccharides and they are synthesised, ultimately from photosynthetic products. In bacteria such polymers are often assembled from exogenous, rather than endogenous disaccharides. 

A wide variety of bacteria synthesize optically active polymers of (P)-3HB and accumulate them as intracellular carbon and energy storage materials. P(3HB) isolated from bacteria is extensively studied as a biodegradable and biocompatible thermoplastic with a melting temperature of SI 80 °C (Figure 9 and Table The crystal stmcture of P(3HB) has already... 

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