Purification and Characterization of an Extracellular Poly( l -Lactic Acid) Depolymerase from a Soil Isolate, Amycolatopsis sp. Strain K104-1

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Abstract
Poly(l-lactic acid) (PLA)-degradingAmycolatopsis sp. strains K104-1 and K104-2 were isolated by screening 300 soil samples for the ability to form clear zones on the PLA-emulsified mineral agar plates. Both of the strains assimilated >90% of emulsified 0.1% (wt/vol) PLA within 8 days under aerobic conditions. A novel PLA depolymerase with a molecular weight of 24,000 was purified to homogeneity from the culture supernatant of strain K104-1. The purified enzyme degraded high-molecular-weight PLA in emulsion and in solid film, ultimately forming lactic acid. The optimum pH for the enzyme activity was 9.5, and the optimum temperature was 55 to 60°C. The PLA depolymerase also degraded casein and fibrin but did not hydrolyze collagen type I, triolein, tributyrin, poly(β-hydroxybutyrate), or poly(ε-caprolactone). The PLA-degrading and caseinolytic activities of the enzyme were inhibited by diisopropyl fluorophosphate and phenylmethylsulfonyl fluoride but were not significantly affected by soybean trypsin inhibitor,N-tosyl-l-lysyl chloromethyl ketone,N-tosyl-l-phenylalanyl chloromethyl ketone, and Streptomyces subtilisin inhibitor. Thus, Amycolatopsis sp. strain K104-1 excretes the unique PLA-degrading and fibrinolytic serine enzyme, utilizing extracellular polylactide as a sole carbon source.