Aflatoxin inhibition of rat liver mitochondrial cytochrome oxidase activity

Area of Science:

• Biochemistry
• Toxicology
• Mitochondrial Function

Background:

• Aflatoxins are toxic secondary metabolites produced by Aspergillus fungi.
• Cytochrome oxidase is a key enzyme in the mitochondrial electron transport chain.
• Understanding aflatoxin effects on cellular respiration is crucial for toxicology.

Purpose of the Study:

• To investigate the inhibitory effects of aflatoxins B1, B2, G1, G2, and M1 on isolated rat liver mitochondrial cytochrome oxidase.
• To determine the mechanism of inhibition, distinguishing between electron transfer and energy transfer processes.

Main Methods:

• Isolated rat liver mitochondria were used.
• Cytochrome oxidase activity was measured using ferrocytochrome c and p-phenylene diamine as reductants.
• Oxygen uptake and substrate oxidation were monitored.
• Oligomycin (respiratory inhibitor) and 2,4-DNP (uncoupler) were used to elucidate the inhibition mechanism.

Main Results:

• All tested aflatoxins inhibited cytochrome oxidase activity.
• Inhibition was more pronounced when measured by O2 uptake compared to substrate oxidation.
• Aflatoxin G2 (AFG2) and Aflatoxin M1 (AFM1) exhibited the highest inhibitory potency (50-70%).
• The results suggest that aflatoxins inhibit electron transfer reactions rather than energy transfer.
• Aflatoxins did not uncouple cytochrome oxidase activity.

Conclusions:

• Aflatoxins B1, B2, G1, G2, and M1 are potent inhibitors of rat liver mitochondrial cytochrome oxidase.
• AFG2 and AFM1 are the most effective inhibitors among the tested aflatoxins.
• The mechanism of inhibition involves interference with electron transfer steps within the enzyme complex.