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Abstract

Substrates linked to a highly fluorescent compound. 4-methylumbelliferone
(MUF), provide a very sensitive system for detecting and quantifying enzyme activity in
aquatic environments. At constant pH, fluorescence of MUF was proportional to MUF
concentration (1-150 nM). However, a more complex relationship between MUF-fluorescence and pH occurred, approaching asymptotes at low (pH less than 3) and high
(pH above 10) pH values, with a sigmoid pattern between pHs of 2 and 13. This pH-
MUF-fluorescence relationship is critical when calculating and comparing enzyme activities measured at different pHs of samples from aquatic environments, and therefore a
measured MUF-fluorescence must be corrected when calculating real enzyme activity
values. The simple correction method when calculating enzyme
activity measured using
methylumbelliferyl substrates at different pH values was determined. The proposed
method was tested for the calculation of exoenzymatic activity measurements of: phosphatase, phosphodiesterase, B-glucosidase. B-galactosidase and protease in lake waters.