Novel Optical Biotest for Determination of Cyanide Traces in Marine Fish Using Microbial Cyanide Hydratase and Formate Dehydrogenase

Abstract.

A novel and simple enzymatic method for the determination of trace cyanide in marine fish is presented. This method is based on the conversion of metal-cyanide complexes by a fungal enzyme extract containing cyanide hydratase (E.C. 4.2.1.66; CyHT) and formamidase (E.C. 3.5.1.49) into formate and ammonia. The formate produced in the sample pretreated with the fungal enzymes was measured by adding formate dehydrogenase (E.C. 1.2.1.2; FDH) and excess NAD⁺. The NADH formed accordingly was monitored at 340 nm. The cyanide calibration curve was found to be linear in the range of 10–100 µM, and the detection limit was 1.1 µM (0.0286 ppm). The proposed biotest was successfully applied to the determination of trace cyanide in a tropical marine food fish species (Russell’s Snapper (Lutjamus russellii)) which had been exposed to cyanide.