Measurement of Low-level Extracellular Enzyme Activity in Natural Waters Using Fluorigenic Model Substrates

Activities of the extracellular enzymes β-D-glucosidase, phosphatase, and leucine aminopeptidase were investigated in unpolluted waters to test the suitability of flu-origenic model substrates for measuring enzyme activities in water samples expected to sustain low levels of activity. The waters tested were surface running waters, shallow ground-waters, and deep groundwaters from water extraction wells. Enzyme activity was detected in all the waters tested, although some of the hydrolytic rates were at the lower limit of current analytical capability. Rates varied between 1.1 and 291 nmol(L.h) for β-D-glucosidase, between 9.2 and 320 nmol(L.h) for phosphatase, and between 5.8 and 1560 nmol(L.h) for leucine aminopeptidase. The method thus proved to be suitable for measuring low levels of extracellular enzyme activity in natural waters, but in any case, it is necessary to adapt the technique to the type of water investigated