FLOW-INJECTION ASSAY OF ENZYME-INHIBITION IN FISH USING IMMOBILIZED DIAMINE OXIDASE

A flow-injection assay for inhibition of diamine oxidase (DAO) is described. Histamine in decomposed fish is detected and used as the enzyme substrate. Sample extracts are doubly injected; one of the two resulting sample zones is passed through a reactor containing DAO immobilized to Sepharose. Histamine is detected sequentially in both the pristine and enzymatically treated zones. The detection chemistry (kinetics-optimized condensation with phthalic dicarboxaldehyde) allows the selective detection of histamine. Subsequent calibration with histamine standard and comparison of the two peak heights allows generic detection of compounds inhibiting the- DAO-mediated conversion of histamine. Preliminary data show that the system can detect inhibitors in extracts of decomposed Mahi-Mahi (associated with a Scombroid poisoning outbreak) and that far lower levels of inhibition are observed in fresh fish. Several known inhibitors and competitive substrates of DAO are also tested.