Characterization of an extracellular poly(3-hydroxyoctanoate) depolymerase from the marine isolate, Pseudomonas luteola M13-4

The characteristics of an extracellular poly(3-hydroxyoctanoate) (PHO) depolymerase purified from the marine isolate Pseudomonas luteola M13-4 were elucidated. The enzyme consisted of a monomeric subunit, having a molecular mass of 28 kDa and isoelectric point of 6.0. The optimum reaction pH and temperature were 10.0 and 40 °C, respectively. Its hydrolyzing activity was significantly inhibited by phenylmethylsulfonyl fluoride (PMSF), suggesting the involvement of a serine as an active site amino acid. The enzyme was able to hydrolyze various types of medium-chain-length poly(3-hydroxyalkanoates) (MCL-PHAs) as well as various chain-length p-nitrophenyl (PNP) esters of fatty acids. The amino acid sequence of the tryptic peptide contained a lipase box pentapeptide sequence, G-I-S-S-G. The N-terminal amino acid sequence of the enzyme exhibited 60–68% similarity to those of other MCL-PHA depolymerases.