The toxicity of 5-chloro-8-hydroxy-3, 4-dihydro-3-methyl-isocoumarin-7-carboxylic acid, a hydrolyzate of ochratoxin A.

Ochratoxin A can be hydrolyzed with a large amount of carboxypeptidase A to yield L-phenylalanine and an isocoumarin carboxylic acid. No hydrolytic effect was found, however, with the liver homogenate or the microsomal fraction of the rat. The toxicity of the hydrolyzate, isocoumarin carboxylic acid, was found to be much lower than that of ochratoxin A (LD50 16.96 ƒÊg/egg) to the chicken embryo; it killed only 3 of 10 chicks when 100 ƒÊg/egg was injected. The hypothesis that ochratoxin A should be hydrolyzed in the liver to exhibit the toxicity, therefore, does not seem to be justifiable.