Purification and properties of versiconal cyclase from Aspergillus parasiticus.

Versiconal cyclase catalyzes the dehydration of versiconal to versicolorin B or versicolorin C [versicolorin B(C)]. The enzyme was purified from mycelia of Aspergillus parasiticus by DEAE-cellulose, hydroxylapatite, and Mono Q column chromatography. The protein contains two identical subunits of molecular weight 72,000 per molecule of native protein. The pI of the enzyme is 3.95. The pH activity curve had a broad maximum with a peak at 5.5. The Km and Vmax for versiconal at 30 degrees C and pH 6.0 are 3.1 microM and 0.15 mumol min-1mg-1, respectively. Most of the formation of versicolorin B(C) in the cell is attributed to the action of versiconal cyclase.