An extracellular poly (3-hydroxybutyrate) depolymerase from Penicillium sp. DS9713a-01

Penicillium sp. DS9713a-01 was obtained by ultraviolet (u.v.) light mutagenesis from the Penicillium sp. DS9713a which can degrade poly (3-hydroxybutyrate) (PHB). The enzymatic activity of DS9713a-01 was 97% higher than that of the wild-type strain. The DS9713a-01 mutant could completely degrade PHB films in 5 days; however, the wild-type strain achieved only 61% at the same time. The extracellular PHB depolymerase was purified from the culture medium containing PHB as the sole carbon source by filtration, ammonium sulfate precipitation and chromatography on Sepharose CL-6B. The molecular weight of the PHB depolymerase was about 15.1kDa determined by SDS-polyacrylamide gel electrophoresis. The optimum activity of the PHB depolymerase was observed at pH 8.6 and 50 degrees C. The enzyme was stable at temperatures below 37 degrees C and in the pH range from 8.0 to 9.2. The activity of PHB depolymerase could be activated or inhibited by some metal ions. The apparent K-m value was 0.164 mg ml(-1). Mass spectrometric analysis of the water-soluble products after enzymatic degradation revealed that the primary product was the monomer, 3-hydroxybutyric acid.