Biodegradation mechanism of polyesters

Poly(alkylene alkanoate)s, such as poly(butylene succinate) (PBS), poly(bulylene adipate) (PBA) and poly(ethylene adipate) (PEA), are synthetic 

8 A plausible mechanism of enzymatic hydrolysis of PBST with lipase PS. The compounds shown in bold are the main products (adapted from Honda et a/,2003). 

were slowly hydrolyzed by a nonspecific mechanism. The PBST degradation was regarded as an endo hydrolysis (Honda et al., 2003). 

2 Poly(lactic acid) and Poly(glycolic acid) 

The intracellular biodegradation pathway of PHB is illustrated and combined with the biosynthetic pathway in Fig. 14.9 (Muller and Seebach, 1993 Senior and Dawes, 1971, 1973 Doi et al, 1992b Haywood et al, 1988). PHB is first depolymerized by PHB depolymerase to produce the 7 -3-hydroxybutyric acid (7 -3-HB) or 7 -3HB oligomers. The latter is further depolymerized by oligomer hydrolase to 7 -3HB monomer. 7 -3HB is dehydrogenated with NAD into acetoacetic acid which follows esterification with CoA-SH to produce acetoacetyl-CoA by the action of acetoacetyl-CoA synthase with the aid of ATP. The acetoacetyl-CoA is degraded into acetyl-CoA by /3-ketothiolase. This compound then enters the tricarboxylic acid (TCA) cycle to transform carbon dioxide and water under aerobic conditions. 

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