HYDROLYSIS OF OCHRATOXIN A BY SOME PROTEOLYTIC ENZYMES

Ochratoxin A, a metabolite produced by a strain of Aspergillus ochraceus and causing enteritis, renal necrosis, an increase of glycogen in the liver when given to rats, as well as inhibiting the phosphorylase enzyme in vitro, is found to be hydrolyzed in vivo to an iso-coumarin derivative (ochratoxin a). The object of this paper is to study the hydrolysis of ochratoxin A by enzymes trypsin, a-chymotrypsin and carboxy-peptidase A. By means of thin layer chromatography on silica gel and spectrophotometric methods such as difference spectra and absorption spectra, it is found that ochratoxin A is hydrolyzed by carboxypeptidase and chymotrypsin. The apparent Km values for the hydrolysis of ochratoxin A by carboxypeptidase and chymotrypsin at 25° are 1.5 × 10-4 M and 1 × 10-3 M, respectively. The first order reaction constants are 1.1 × 10-2 and 7.6 × 10-3 min-1, while the apparent proteolytic coefficients are 4.4 and 0.01, respectively. These results indicate that ochratoxin A has a much greater affinity for carboxy-peptidase A than for a-chymotrypsin. It is suggested that ochratoxin A is hydrolyzed in vitro by carboxypeptidase A and a-chymotrypsin and possibly cathepsin C from lyosomes. © 1969.