Protein-binding Potential of Ochratoxin A in vitro and Its Fluorescence Enhancement

The binding potential of ochratoxin A (Oct. A), a carcinogenic mycotoxin detected in cereals and proteinous products, to animal tissue and serum proteins in vitro was investigated to get basic information on its toxicity. The relationship between the binding potential and fluorescence enhancement of Oct. A in the presence of serum albumin is also discussed. Oct. A had a high affinity to serum albumin but little affinity to soluble tissue proteins of liver and kidney in the rat as determined by electrophoretic analysis. Human serum albumin (HSA) had a much higher affinity for Oct. A than did α1-, α2-, β- and γ-globulins. The binding parameters to HSA were n=2.15±0.05 and K=6.01±0.09 (×105/M). The fluorescence enhancement of Oct. A in the presence of HSA was pH-dependent and increased from pH 4.0, reaching a maximum at pH 5.0. These data were similar to those for bovine serum albumin (BSA). The enhancement was not connected with major binding at a carboxyl group of Oct. A but probably with a weak interaction between an isocoumarin ring of Oct. A and the albumin protein.