FIG. 1.

Schematic representation of the late steps in aflatoxin biosynthesis and postulated enzymatic steps involved in aflatoxin G₁ and G₂ production in A. parasiticus. The simplified scheme shows the formation of aflatoxins B₁, G₁, B₂, and G₂, starting from polyketide and branching at Ver B. The precursors of aflatoxins B₁ and G₁ are Ver A, ST, and OMST, and the precursors of aflatoxins B₂ and G₂ are DHST and DHOMST. The ordA gene product, a cytochrome P-450 monooxygenase, is capable of converting OMST to aflatoxins B₁ and G₁ and DHOMST to aflatoxins B₂ and G₂. It has been proposed (indicated by question marks) that at least one additional enzyme is required for the production of aflatoxins G₁ and G₂ from postulated intermediates (5). Me, methyl group.