Biochemical Studies on Ochratoxin A

  • M. J. Pitout


Ochratoxin A is one of three chemically related metabolites isolated from Aspergillus ochraceus Wilh. 1 It has been structurally characterised as 7-carboxyl-5-chloro-8-hydroxy-3,4-dihidro-methylisocoumarin linked over its 7-carboxyl group to L-β-phenylalanine.2 The LD50 in rats dosed per os is 20 mg/kg and the toxin causes enteritis, renal necrosis and an increase in the quantity of glycogen in rat liver.3 The route and time course of the metabolism of ochratoxin A was investigated by Nel and Purchase4 in view of the fact that the increase in glycogen only became evident 4 to 5 days after dosing. They concluded that ochratoxin A is hydrolysed in vivo to the isocoumarin moiety (ochratoxin α) most probably by proteolytic enzymes.

Fig 1

Fig. 1. A chromatogram of ochratoxin A before and after hydrolysis with carboxy- peptidase A, α-chymotrypsin and trypsin. A standard mixture of ochratoxins A and α is illustrated by 1, while 2, 3, 4 and 5 represent ochratoxin A before hydrolysis and after reaction with carboxypeptidase, chymotrypsin and trypsin, respectively. Hydro-lysis was performed at 25° for 5 min and the concentrations of ochratoxin A, carboxy- peptidase, chymotrypsin and trypsin were 1.5 × 10−4 M, 50 μg/ml, 300 µg/m1 and 300 µg/ml, respectively (from ref. 6).


Proteolytic Enzyme Aromatic Amino Acid Glycogen Storage Disease Peptide Linkage Phenylpropionic Acid 
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© South African Medical Research Council 1971

Authors and Affiliations

  • M. J. Pitout
    • 1
  1. 1.Division of ToxicologyNational Institute for Nutritional Diseases South African Medical Research CouncilSouth Africa

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