Biodegradation mechanism of naturally occurring polymers

Proteins and carbohydrates are the most important and renewable biological polymeries which are frequently used in the industrial and medicinal fields. Most enzymes catalyzing the primary degradation of protein and carbohydrates are hydrolase enzymes. Apart from these polymers, a relatively lower amount of natural polymers such as natural rubber, nucleic acids and lignin, are available. In this section, the biodegradation mechanisms of the more abundant and well-known natural polymers, such as proteins, cellulose, starch, chitin, chitosan, nucleic acids, and their derivatives, are omitted because many excellent reviews and books are available. 

Proposed degradation mechanism of the double bond of poly(c/.v-l,4-isoprene) 

5 Proposed degradation mechanism of natural rubber and final product (adapted from Tsuchii and Takeda, 1990 Lions and Steinbuchel, 2001). 

Among the synthetic rubbers, only poly(cw-l,4-isoprene) rubber has been reported to be biodegradable. It is also known that poly(cA-l,4-isoprene) is quite susceptible to oxidative degradation at the double bond. Thus, carbonyl ends are produced by the double bond scission as shown in Fig. 14.5 (Harayama et al, 1992). As shown in this figure, double bond cleaving dioxygenases require a transition metal as a cofactor for their interaction with dioxygen. 

Coals are complex and heterogeneous polymer networks with aliphatic and ether bridges between aromatic moieties. There are two different bioconversion 

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