An Extracellular Poly(3‐Hydroxybutyrate) Depolymerase from Alcaligenes faecalis

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Abstract
A strain of Alcaligenes faecalis T1, which was isolated from activated sludge, excreted an extracellular poly(3-hydroxybutyrate) depolymerase as it grew in a medium containing poly(3-hydroxybutyrate) as the sole carbon source. The molecular weight of the enzyme, purified from the culture medium to electrophoretic homogeneity, was 48000 as determined by Sephadex G-100 filtration, and 50000 by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. The pH optimum for the enzyme reaction was 7.5. The purified enzyme depolymerized poly(3-hydroxybutyrate) purified from Zoogloea ramigeva 1–16-M, but did not attack the bacterial native poly(3-hydroxybutyrate containing granules. K, values were 13.3 μpg/ml(= 0.78 μM, based on an estimated average molecular weight of 17000) for poly(3-hydroxybutyrate) and 5.4mM for the trimeric ester of D(–)-3-hydroxybutyric acid. Analysis of hydrolytic products of poly(3-hydroxybutyrate), several oligomeric esters of D(–)-3-hydroxybutyric acid, and the methyl ester of the trimeric ester indicated that the enzyme hydrolyzed these substrates from the free hydroxyl terminus, releasing D(-)-3-hydroxybutyrate dimer units one at a time.