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

Abstract

A strain of Alcaligenes faecalis T 1, 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.