Abstract
Streptomyces antibioticus NF-18 is a hyperproducing strain of a Streptomyces hormone, virginiae butanolide A (VB-A), that induces virginiamycin production of S. virginiae at nanomolar concentrations. To characterize the biosynthetic pathway of VB-A, we identified and characterized for the first time the 6-dehydroVB-A reductase that is responsible for the final reduction step in the biosynthesis. Assay protocols and stabilization conditions were established. The 6-dehydroVB-A reductase was found to require NADPH, not NADH, as a coenzyme. The K m values of the enzyme for NADPH and (±)-6-dehydroVB-A were determined to be 50±2 μM and 100±5 μM, respectively. Ultracentrifugation experiments revealed that 6-dehydroVB-A reductase was present almost exclusively in the 100 000× g supernatant fraction, indicating that the enzyme is a cytoplasmic-soluble protein. The M r of the native 6-dehydroVB-A reductase was estimated to be 82 000±3000 by molecular sieve HPLC. The optimal pH was found to be 6.7±0.2.
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