Purification and characterization of a novel FMN-dependent enzyme. Membrane-bound L-(+)-pantoyl lactone dehydrogenase from Nocardia asteroides

Membrane-bound L-(+)-pantoyl lactone dehydrogenase, an enzyme that catalyzes the formation of ketopantoyl lactone from L-(+)-pantoyl lactone, was solubilized with Brij 35 and purified 78-fold to apparent homogeneity, with a 3.7% overall recovery, from Nocardia asteroides through purification procedures including successive ammonium sulfate fractionation, and DEAE-Sephacel, Sepharose CL-6B and Cellulofine GC-700-m column chromatography in the presence of Brij 35. The relative molecular mass of the native enzyme, as estimated on high-performance gel-permeation chromatography, is at least more than 600 kDa and its subunit molecular mass is 42 kDa. The enzyme shows high specificity for L-(+)-pantoyl lactone as a substrate (Km = 26.8 mM; Vmax = 4.22 mumol.min-1.mg protein-1). Brij 35 acts as a stabilizer and also as an efficient activator of the enzyme. The prosthetic group of L-(+)-pantoyl lactone dehydrogenase was identified as noncovalently bound FMN.