- Aflatoxins B₁, Q₁ and aflatoxicol, R [subscript o] F, but not B₂ were activated in the presence of NADPH by the 105,000 x g pellet from rainbow
trout (Salmo gairdneri), Mt. Shasta strain, liver to products lethal to
Bacillus subtilis GSY 1057 (metB4, hisAl, uvr-1). Electron microscopy
confirmed the microsomal fraction primarily contained smooth
endoplasmic reticulum. An NADPH mixed function oxidase with neo-tetrazolium
reductase and aldrin epoxidase activity was present in the
microsonaes. The activity of the oxidase was reduced parallel to a
decrease in lethal factor production by piperonyl butoxide, NADPH
deprivation, heat treatment and certain diets. After incubation of
microsomes with ¹⁴C labeled B₁, the activity was found in unaltered
B₁ and three extremely polar metabolites designated NM (3. 6-5. 3%),
B [subscript 2a] A (1-5%) and M₁A (< 1%). They were eliminated or reduced along
with microbial lethality when cytosine and cysteine were added to the
The structural requirement for the vinyl ether of B₁, R [subscript o] F and
Q₁ and the nature of the enzymatic reaction were consistent with the
hypothesis that the conapounds were metabolized to highly reactive and
unstable electrophilic products which bound to nucleophiles such as
cytosine and were lethal to B. subtilis.
Aflatoxicol, R [subscript o] F, was isolated from liver homogenates and was
apparently fornaed by an NADPH-dependent soluble enzyme of the
105,000 x g supernatant from rainbow trout. R [subscript o] F and its diastereomer, R [subscript o] R, were prepared by chemical reduction of B₁. Their
identity was confirmed by UV and mass spechrometry. The ten-day
LD50 value was 0.66 mg/kg for R [subscript o] F compared to 0.46 mg/kg for B₁.
No mortality was observed, from R [subscript o] R at equivalent doses. Similar
gross and microscopic pathological changes were observed for B₁,
R [subscript o] F and R [subscript o] R. The degree of damage paralleled the LD50 values.
After eight months of feeding, 20 ppb of B₁ and R [subscript o] F and 36.6 ppb
R [subscript o] R gave 56.3%, 26.2% and 0% incidence of hepatoma. Addition of
50 ppm of cyclopropenoid fatty acids increased the incidence to 96.3%,
93.8% and 55% for B₁, R [subscript o] F and R [subscript o] R.
It was concluded that aflatoxicol was not an effective means of
detoxication of B₁, but instead extended the presence of a potentially
toxic and carcinogenic compound.