Involvement of Catalytic Amino Acid Residues in Enzyme-Catalyzed Polymerization for the Synthesis of Polyesters

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)-β-butyrolactone
(BL) were compared. BL was polymerized at 80 °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.