Microbial degradation of polyurethane, polyester polyurethanes and polyether polyurethanes.

Polyurethane (PUR) is a polymer derived from the condensation of polyisocyanate and polyol and it is widely used as a base material in various industries. PUR, in particular, polyester PUR, is known to be vulnerable to microbial attack. Recently, environmental pollution by plastic wastes has become a serious issue and polyester PUR had attracted attention because of its biodegradability. There are many reports on the degradation of polyester PUR by microorganisms, especially by fungi. Microbial degradation of polyester PUR is thought to be mainly due to the hydrolysis of ester bonds by esterases. Recently, polyester-PUR-degrading enzymes have been purified and their characteristics reported. Among them, a solid-polyester-PUR-degrading enzyme (PUR esterase) derived from Comamonas acidovorans TB-35 had unique characteristics. This enzyme has a hydrophobic PUR-surface-binding domain and a catalytic domain, and the surface-binding domain was considered as being essential for PUR degradation. This hydrophobic surface-binding domain is also observed in other solid-polyester-degrading enzymes such as poly(hydroxyalkanoate) (PHA) depolymerases. There was no significant homology between the amino acid sequence of PUR esterase and that of PHA depolymerases, except in the hydrophobic surface-binding region. Thus, PUR esterase and PHA depolymerase are probably different in terms of their evolutionary origin and it is possible that PUR esterases come to be classified as a new solid-polyester-degrading enzyme family.

Isolation and characterization of a bacterium which utilizes polyester polyurethane as a sole carbon and nitrogen source.

Various soil samples were screened for the presence of microorganisms which have the ability to degrade polyurethane compounds. Two strains with good polyurethane degrading activity were isolated. The more active strain was tentatively identified as Comamonas acidovorans. This strain could utilize polyester-type polyurethanes but not the polyether-type polyurethanes as sole carbon and nitrogen sources. Adipic acid and diethylene glycol were probably the main degradation products when polyurethane was supplied as a sole carbon and nitrogen source. When ammonium nitrate was used as nitrogen source, only diethylene glycol was detected after growth on polyurethane.

Changes of collagen types at various stages of human liver cirrhosis.

Macromolecular collagen components in normal liver and at the different stages of human liver cirrhosis were studied under various extraction conditions. The collagen content at the typical stage of liver cirrhosis was more than five-fold higher than that of the normal state. Pepsin-solubilized collagens extracted successively accounted for 90% of the total collagen and were subjected to determination of the collagen types by salt differentiated fractionation and SDS-polyacrylamide gel electrophoresis. Both type I and III collagens, especially the former, increased, reflecting enhanced total collagen with the progression of liver cirrhosis. The ratio of type I to type III was 1.02 - 1.22 in normal liver and at the early stage of liver cirrhosis, but increased to 1.58 and 1.60 at the typical and advanced stages of liver cirrhosis, respectively. At the early stage, the remarkable increase in type V collagen started much earlier than at the typical stage when the ratio of type I to type III changed. The enhancement of type V collagen may result from a cell proliferative phenomenon at the earlier stage of liver cirrhosis.