Application of cyanide-metabolizing enzymes to environmental control; enzyme thermistor assay of cyanide using immobilized rhodanese and injectase

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Abstract
The application of the enzyme thermistor in the analysis of cyanide in standard solutions as well as in blast furnace waste water is described. The heat signal is generated in the conversion of cyanide, catalyzed by the immobilized enzymes rhodanese (E.C. 2.8.1.1) and injectase (E.C. 4.4.19). Using the combination of cyanide‐metabolizing enzymes and the enzyme thermistor unit, assays down to 20μM cyanide can be carried out. Linear relationships were obtained at 20–600μM cyanide for injectase and 20–1000μM for rhodanese. The stability at 27°C of the heat response was initially decreased, but soon stabilized at about 80% of the initial value and remained so for at least 200 hr. The technique was easily adapted to continuous analysis, applicable to environmental control (e.g., a “cyanide guard”) with a response time at present within 2–3 min after a sudden change in cyanide concentration has appeared.