title: Involvement of catalytic amino acid residues in enzyme-catalyzed polymerization for the synthesis of polyesters.
abstract: Recently, a variety of aliphatic polyesters have been synthesized using hydrolases such as lipases and PHB depolymerases, and the reaction mechanism for these enzyme-catalyzed polymerization has been discussed. In this paper, we have studied the involvement of the catalytic amino acid residues of the hydrolase in enzyme-catalyzed polymerization with an extracellular PHB depolymerase from Alcaligenes faecalis T1. A wild-type PHB depolymerase and three kinds of site-specific mutants (catalytic amino acids were substituted) were prepared and their polymerization activities for the ring-opening polymerization of (R)-beta-butyrolactone (BL) were compared. BL was polymerized at 80 degrees C in bulk by the wild-type enzyme to yield polymers consisting of cyclic and linear structures in a high monomer conversion. In contrast, none of the mutant enzymes showed obvious polymerization activity. These results have clearly demonstrated that the catalytic triad is indeed responsible for the enzyme-catalyzed polymerization of BL.
authors.affiliation: Polymer Chemistry Laboratory, RIKEN Institute, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.forename: S
authors.initials: S
authors.lastname: Taguchi
authors.forename: T
authors.initials: T
authors.lastname: Saito
authors.forename: K
authors.initials: K
authors.lastname: Toshima
authors.forename: S
authors.initials: S
authors.lastname: Matsumura
authors.forename: Y
authors.initials: Y
authors.lastname: Doi
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives* / Q000737:chemistry*; D000421:Alcaligenes / Q000201:enzymology* / Q000235:genetics; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry* / Q000235:genetics; D002384:Catalysis; D016297:Mutagenesis, Site-Directed; D011091:Polyesters / Q000737:chemistry*
chemical_list: D011091:Polyesters; C013426:beta-butyrolactone; D002265:Carboxylic Ester Hydrolases; C022417:poly-beta-hydroxybutyrate depolymerase; D015107:4-Butyrolactone