TRACING OF PEROXIDASE-ACTIVITY IN HUMIC LAKE WATER

An enzyme assay was developed for studies on peroxidase activities in humic lake water. 3,4-Dimethoxybenzyl alcohol (veratryl alcohol, VeraO H) was used as tracer substrate, and peroxidase (EC 1.11.1.7) activity was measured by highperformance liquid chromatography. The chemical s tability of VeraOH and its application as peroxidase substrate was tes ted under light and dark conditions, different hydrogen peroxide (H2O2 ) concentrations and humic matter contents. VeraOH was stable under lo w UV radiation at in situ conditions in lake water (<0.010...0.25 kJ m (-2) d(-1)), laboratory conditions (<0.05...0.30 kJ m(-2) d(-1)), and low (1...100 mu M) H2O2 concentrations. However, peroxides oxidized Ve raOH above 1...10 mM H2O2 concentration in sterile Millipore-Q and hum ic lake water. Dark incubations showed little VeraOH oxidation product s. The developed peroxidase assay was tested in the growth medium of P hanerochaete chrysosporium and a bacteria isolate (P.M.D. 20.4.3.1) fr om mesohumic lake Paajarvi. Peroxidase activities were also measured i n natural microbial communities under standard laboratory and under in situ conditions in humic lake water. Incubation times of about 5 to 1 2 days were usually needed to record significant (P < 0.05) peroxidase activities in lake waters. In situ peroxidase activities varied in pe lagial surface water (0...0.5 m) on a seasonal scale between 74 nmol L -1 h(-1) and 273 nmol L-1 h(-1) (mean: 176 nmol L-1 h(-1)) and within the water column between 110 nmol L-1 h(-1) and 800 nmol L-1 h(-1) (me an: 500 nmol L-1 h(-1)) in polyhumic lake Mekkojarvi.