Hydrolase activity of an extracellular depolymerase from Aspergillus fumigatus with bacterial and synthetic polyesters

An extracellular depolymerase produced by the fungus Aspergillus fumigatus was found to have hydrolytic activity towards both bacterial and synthetic polyesters. The enzyme catalysed the hydrolysis of the bacterial polyesters: poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/HV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB/4HB) over the entire range of compositions. In addition, this fungal depolymerase also catalysed the hydrolysis of synthetic, aliphatic polyesters including poly(ethylene adipate) (PEA), poly(ethylene succinate) (PES), poly(1,4-tetramethylene adipate) (PTMA) and several commercial poly(ester urethanes) with the trade name "Bionolle." However, the enzyme was inactive for other synthetic polyesters, including poly([R]-lactide), (P[R]-LA), poly(5-valerolactone) (PVL) and poly(6-caprolactone) (PCL). The results on enzyme specificity and activity, and the types of degradation products obtained, were analyzed by molecular modelling. The analysis indicated that there is a relationship between the activity of the depolymerase, as indicated by the relative rates of hydrolysis of the different polyesters, and the molecular dimensions of their repeating units. (C) 1999 Elsevier Science Ltd. All rights reserved.