The toxicity of alfatoxin B2a (hydroxydihydro-aflatoxin B1) was studied in several biological systems. Aflatoxin B2a is the monohydroxylated derivative obtained from addition of water to the double bond of the terminal furan of B1. Examination of the sensitivity of a group of microorganisms to B2a demonstrated that the inhibitory spectrum was similar to aflatoxin B1. However, the toxicity of B2a was markedly lower than B1, as measured by the initiation of bile duct hyperplasia in ducklings. Binding of aflatoxin to deoxyribonucleic acid (DNA) was determined by measuring the hypochromicity produced by the nucleic acid at 363 nm and the capacity of increasing amounts of DNA to quench the fluorescence of the toxin was also used as a measure of the binding of toxin to nucleic acid. These tests showed that the DNA-binding capacity of B2a was lower than B1.
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