Abstract
We have compared 2 methods for preparing radiolabeled aflatoxins from [14C] acetate for use in biosynthetic studies at the end of the aflatoxin pathway. The Salhab‐Edwards method (SE) used a 3‐day‐old mycelium and a defined medium containing MnCl2 with incubation at 28 C. The Lee‐Bennett method (LB) used a 2‐day‐old mycelium and a defined medium containing low levels of Mn with incubation at 30 C. Generally, the LB method produced lower quantities of aflatoxin but the product had higher specific activities (sp act). The SE method produced 0.157μmol of aflatoxin B1 and 0.028μmol of G1 compared to the LB method with 0.058μmol of aflatoxin B1 and 0.001μmol of G1. The sp act (inμCi/μmol) for aflatoxin produced by the LB method were: B1 = 1.379; B2 = 0.130; G1 = 5.0 and G2 ‐ 0.063. The sp act of aflatoxin produced by the SE method were: B1 = 0.267; B2 = 0.014; G1 = 0.178; and G2 =0.133. Unlabeled aflatoxins were presented to resting cell cultures of the versicolorin‐A‐accumulating mutant ofAspergillus parasiticus. No conversion of aflatoxin B, was noted. However, when aflatoxins B2 or G1 were presented low levels of aflatoxins B1 and G2 were recovered. Aflatoxins B2 and G1 were recovered when aflatoxin G2 was presented. Similar low levels of recovery were obtained in experiments using autoclaved mycelia. Thus we conclude that these minor quantities of aflatoxins recovered were not produced enzymatically.