Enzymes and aflatoxin biosynthesis.

The enzymology of secondary metabolism has not received the same attention as that for primary (general) metabolism. There are traditional and other reasons for this bias, some of which will become apparent in this review. With the advent of recombinant deoxyribonucleic acid technology (genetic engineering), it seems inevitable that this state of affairs should change. Many secondary metabolites have economic significance, and it would be very desirable to be able to manipulate their production by using this latest technology. Strictly speaking, it is not impossible to do this without a knowledge of the enzymes involved in their production, but in practice it is essential that we have thorough and detailed information on the enzymes (and their regulation) that we would desire to manipulate. The truth of this statement is well supported by the increased interest in the enzymes responsible for the formation of secondary metabolites of commercial importance (93, 116, 135). The field of antibiotics is a particularly good example of this groundswell and includes work on penicillin (103), tetracycline (104), tylosine (129), and bacitracin (158). Another group of secondary metabolites of economic impact are the mycotoxins, although it is implicit in their nature that we should try to prevent, rather than promote, their formation. An important example of mycotoxins, the aflatoxins, have generated much interest in both their effects and their biosynthesis; investigations into the latter have led to elucidation of the pathway of their formation (16). In spite of agreement on the validity of this pathway, there is still much to be learned with respect to the enzymology of the process. This review attempts to bring together what is known with regard to these enzymes and their regulation and associated processes and also to stimulate further interest in the subject. FUNGAL SECONDARY METABOLIC ENZYMES