ポリ-3- ヒドロキシ酪酸の代謝

概要

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Poly-3-hydroxybutyrate (PHB) is a biopolyester synthesized by a wide range ofbacteria, as well as by some Archaea, and is deposited as insoluble cytoplasmic inclusions. An overview of the metabolism of PHB inside and outside the cell is provided. The first extracellular PHB depolymerase gene was cloned from Ralstonia pickettii T1. The enzyme is composed of catalytic, linker, and PHB-binding domains. At present, extracellular PHA depolymerase structural genes from different bacteria have been cloned and the nucleotide sequences havebeen obtained. The first intracellular PHB depolymerase gene was cloned from Ralstonia eutropha H16. Mutation of the gene reduced degradation PHB efficiently, but did not inhibit all hydrolytic activity, suggesting the existence of an other enzyme(s). Other intracellular PHB depolymerases have been researched and we found three different depolymerases based on the similarity of their amino acid sequences with extracellular PHB-degrading enzymes. In addition, a novel reaction, thiolysis of PHB with coenzyme A, was found and the thiolysis of PHB was the dominant reaction in PHB inclusions in R. eutropha H16. Different algorithms suggest that PHB depolymerase belong to the alpha/beta-hydrolase superfamily, with a conserved serene or cysteine residue as a catalytic nucleophile.
2009-10-20