Positive correlation exists between glutathione S-transferase activity and aflatoxin formation in Aspergillus flavus

Abstract

The presence of glutathione (GSH) S-transferase activity, using 1-chloro-2,4-dinitrobenzene (CDNB) as a substrate, has been established in the cytosolic fraction of the toxigenic (aflatoxin producing) and non-toxigenic strains of Aspergillus flavus. Significant differences in the GSH S-transferase activity were observed between the toxigenic and non-toxigenic strains. A positive correlation has been demonstrated for the first time between aflatoxin formation and a biochemical parameter, namely GSH S-transferase activity. The evidence in support of A. flavus GSH S-transferase induction by endogenous aflatoxins is as follows: (i) the age-related production of aflatoxin follows the same pattern as the cytosolic GSH S-transferase activity profile; (ii) significantly higher enzyme activity was associated with mycelia of a toxigenic strain grown in medium supporting high aflatoxin production (sucrose-low salts medium) while the enzyme activity was low in medium producing less aflatoxin (glucose-ammonium nitrate medium). The GSH S-transferase activity of the non-toxigenic strain was hardly affected by a change in the medium as it produces no aflatoxins; and (iii) the toxigenic strain demonstrated significantly higher apparent (V(max.)) with no change in K(m) as compared with the non-toxigenic strain. This indicates that enzyme induction by endogenous aflatoxins is similar to the action of phenobarbital and other inducing drugs (Kaplowitz et al., 1975).