Mycopathologia 113: 41-44, 1991. 9 1991 Kluwer Academic Publishers. Printed in Belgium. The appearance of an enzyme activity catalysing the conversion of norsolorinic acid to averantin in Aspergillus parasiticus cultures Anil A. Chuturgoon & Michael F. Dutton Department of Biochemistry, University of Natal, Pietermaritzburg, 3200 Natal, South Africa Received 30 October 1989; accepted in revised form 11 June 1990 Key words: Aspergillus parasiticus, averantin, norsolorinic acid, secondary metabolic enzyme Abstract The activity of the enzyme responsible for the conversion of norsolorinic acid to averantin was studied in two strains ofAspergillusparasiticus. Cell-free extracts of the enzyme were purified from different aged mycelia and little activity was found prior to 24 hours after inoculation but this quickly reached a maximum at 48 hours and declined thereafter. Both strains ofA. parasiticus, one in aflatoxin producing strain, the other a versicolorin A accumulating mutant, showed this trend. It was concluded that the enzyme responsible for this conversion was a secondary metabolic enzyme and was distinct from alcohol and mannitol dehydrogenases. Introduction Early elucidation of the mechanisms of aflatoxin biosynthesis centred on the establishment of intermediates in the pathway [ 1]. The identities of several intermediates were determined using radio-isotopes, nuclear magnetic resonance spec- troscopy with stable isotopes and mutants of Aspergillus parasiticus [2, 3]. Regulation of the pathway involves complex controls, which are strongly influenced by specific cellular events in the growth cycle [4, 5]. Current research has concentrated on the ter- minal enzyme catalysed steps of aflatoxin B 1 (AFB1) biosynthesis, i.e., the conversion of sterigmatocystin (ST) to O-methylsterigmatocys- tin (OMST) [6, 7] and both these substrates to AFB l. The enzymes responsible for the earlier steps in the pathway have received less attention. Consequently we are currently studying the en- zyme [8] responsible for the conversion of nor- solorinic acid (NA) to averantin (AVN) (Fig. 1). Both these metabolites have been identified as intermediates in aflatoxin biosynthesis [ 1, 9]. In this study the activity of the enzyme, respon- sible for the conversion of NA to AVN, during the life cycle of A. parasiticus is investigated. Materials and methods The metabolites NA and AVN were isolated and purified [9, 10] from mutants of A. parasiticus (NOR-1) and (ver-mu-39) both kindly donated by Dr J.W. Bennett, University of Tulane. A versi- colorin A accumulating mutant of A. parasiticus (1-11-105 Whl) also supplied by Dr Bennett and an aflatoxin producing strain of A. parasiticus