A RAPID SPECTROPHOTOMETRIC METHOD FOR ASSAY OF CARBOXYPEPTIDASE A

A novel method is described for the determination of the activity of carboxypeptidase A. Ochratoxin A, an isocoumarin derivative linked over its 7-carboxygroup to l-β-phenylalanine, is found to be hydrolysed in vitro to ochratoxin a by pancreatic carboxypeptidase. Ochratoxin A has an absorption peak at 380 mμ at pH 7.5 while ochratoxin a has only an absorption peak at 330 mμ at the same pH. When ochratoxin A is hydrolysed by means of HCl or carboxypeptidase A the absorption peak at 380 mμ disappears while a peak at 330 mμ appears. Difference and absorption spectra indicate that the decrease at 380 mμ is much more sensitive than the increase of absorption at 330 mμ. It is also found that the spectrophotometric assay method (measuring the decrease at 380 mμ) is much more sensitive than the colorimetric ninhydrin method. © 1969.