Solubilization, Purification, and Properties of Membrane-Bound D-Glucono-δ-lactone Hydrolase from Gluconobacter oxydans

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Membrane-bound glucono-δ-lactonase (MGL) was purified to homogeneity from the membrane fraction of Gluconobacter oxydans IFO 3244. After solubilization with 1 M CaCl₂, MGL was purified in the presence of Ca²⁺ and detergent. A single band corresponding to 60 kDa appeared in SDS–PAGE. The molecular weight of MGL was judged to be 120k. Differently from cytoplasmic lactonases, MGL showed optimum pH in an acidic range of 5–5.5. It was highly sensitive to metal-chelating agents such as EDTA, and the lost MGL activity was restored to the original level by the addition of divalent cations such as Ca²⁺ or Mg²⁺. The purified MGL was strictly dependent on Ca²⁺ and underwent rapid denaturing precipitation on Ca²⁺ depletion even in the presence of detergent. This communication can be the first one dealing with the solubilization, purification and properties of MGL.