Purification and Characterization of Acetoacetyl‐CoA Synthetase from Zoogloea ramigera I‐16‐M

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Abstract
Acetoacetyl‐CoA synthetase was purified to electrophoretic homogeneity from Zoogloea ramigera I‐16‐M, a poly(3‐hydroxybutyrate)‐accumulating bacterium, which lacks 3‐ketoacid CoA‐transferase. The purified enzyme had a specific activity of 52.2 μmol acetoacetyl‐CoA formed min−1 mg protein−1, which constituted a 680‐fold purification compared to the crude extract, with a 5.1% yield. The enzyme absolutely required ATP, CoA, a monovalent cation (K+, Rb+, Cs+ or NH+4) and a divalent cation (Mg2+, Mn2+, Ca2+ or Ni2+) for the activation of acetoacetate, yielding acetoacetyl‐CoA, AMP and pyrophosphate in equimolar amounts. The pH optimum of the enzyme reaction was 8.4. The molecular weight of the enzyme was approximately 70000 as estimated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, and 72000 by Sephadex G‐200 gel filtration. The enzyme was active only on acetoacetate and to a lesser extent on l(+)‐3‐hydroxybutyrate, and the Km values for acetoacetate, l(+)‐3‐hydroxybutyrate, ATP and CoA were 7.6 × 10−5 M, 1.4 × 10−3 M, 3.3 × 10−5 M and 9.1 × 10−5 M respectively.