Nylon is a widely used synthetic polymer found in a variety of products, including carpeting, fabrics, electrical parts, and many other plastic applications. Total annual production is about 5.5 million tons worldwide. There are several variations of the polymer, the two most common being nylon 6 and nylon 6,6 (Wikipedia Nylon).
Nylon is not considered a hazardous chemical, although its accumulation in landfills renders it a desirable recyclable commodity. Some investigation is under way as to whether nylon dust causes respiratory illness in those exposed to it (Warheit et al., 2001). Furthermore, the synthesis of adipic acid, a chemical used in production of nylon-6,6, produces large emissions of nitrous oxide. Nitrous oxide has a stronger greenhouse effect than carbon dioxide (about 200 times), and is also thought to contribute to ozone layer degradation (Wikipedia Nitrous Oxide).
The initial step in the degradation of nylon involves the transport of the compound across the outer membrane of the cell. Nylon 6 exists as a polymer in excess of 100 units. A few different enzymes are known to degrade nylon oligomers via different mechanisms. The endo-type hydrolases can cleave the oligomer in the middle of the molecule, and the exo-type hydrolase can only remove 6-aminohexanoyl groups from the N-terminus. The endo-type 6-aminohexanote oligomer hydrolase can degrade oligomers up to 20 units. It degrades oligomers into various sizes depending on which amide bond is hydrolized (Kakudo et al., 1993). The nylon linear dimer hydrolase is exo-type and can slowly degrade oligomers up to 6 units (Negoro et al., 1983). Thus, the following pathway could start with the hexamer and follow a slightly different order of successive oligomer metabolites, depending on the enzyme.
The following is a text-format Nylon Oligomer Pathway Map using the pathway of the exo-type 6-aminohexanoic acid oligomer hydrolase (synonomous with 6-aminohexanote-dimer hydrolase) to degrade nylon 6. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (3k) format.
6-Aminohexanoate hexamer Pseudomonas sp. NK87 Flavobacterium sp. KI72 | | 6-aminohexanoate- | dimer hydrolase | v 6-Aminohexanoate pentamer 6-Aminohexanoate cyclic dimer | Pseudomonas syringae PSPTO4526 | Burkholderia mallei BMA2839 | 6-aminohexanoate- Mesorhizobium loti mlr4825 | dimer hydrolase Bradyrhizobium japonicum blr7282 | Rhodopseudomonas palustris CGA009: RPA2974 v Rhodopseudomonas palustris CGA009: RPA3959 6-Aminohexanoate tetramer Caulobacter crescentus CC1323 | Silicibacter pomeroyi SPO2527 | Bacillus licheniformis DSM13: BLi00325 | 6-aminohexanoate- Streptococcus mutans SMU.1218 | dimer hydrolase Mycobacterium avium paratuberculosis MAP0581c | Nocardia farcinica nfa18760 v Nocardia farcinica nfa28320 6-Aminohexanoate trimer Streptomyces coelicolor SCO7601 SC7H9.13C | | | 6-aminohexanoate- | 6-aminohexanoate- | dimer hydrolase | cyclic dimer hydrolase | | v | 6-Aminohexanoate <--------------------------+ linear dimer | | 6-aminohexanoate- | dimer hydrolase | v 6-Aminohexanoate | | | | v to the Caprolactam Pathway
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