Extracellular poly(hydroxyalkanoate) depolymerases and their inhibitor from Pseudomonas lemoignei

Abstract

Enzymatic degradation processes of microbial copolyesters, poly(3-hydroxybutyrate-co-3-hydroxyvalerate): P(3HB-co-3HV) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate): P(3HB-co-4HB), were studied by the weight loss (erosion) of copolyester films. These studies employed three extracellular depolymerases which degrade poly(3-hydroxybutyrate): P(3HB). Two enzymes were purified from the culture supernatant of Pseudomonas lemoignei and one from Alcaligenes faecalis T1. The rate of enzymatic degradation of microbial copolyester films with various compositions showed an almost similar tendency to three different P(3HB) depolymerases, and decreased in the following order: P(3HB-co-4HB) greater than P(3HB) greater than P(3HB-co-3HV). An inhibitory protein of P(3HB) depolymerases in the succinate culture medium of P. lemoignei was isolated and characterized. The molecular weight of P(3HB) depolymerase inhibitor was 35,000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. This inhibitor of a single polypeptide chain may reversibly bind the serine residues at the active site of P(3HB) depolymerase. This inhibitory protein was not induced in the culture medium when P. lemoignei was grown on P(3HB) as the sole carbon source.