USE OF PERFUSED CORES FOR EVALUATING EXTRACELLULAR ENZYME-ACTIVITY INSTREAM-BED SEDIMENTS

beta-Glucosidase activity was investigated in stream-bed sediments usi ng 4-methylumbelliferyl-beta-D-glucopyranoside (MUF-beta-Glc) as a mod el substrate. In a perfused core technique, water containing MUF-beta- Glc was perfused up through sediment cores. beta-glucosidase activity was quantified from the release of fluorescent MUF in water discharged from the cores. At low rates of perfusion, maximum beta-glucosidase a ctivity (V-max) in perfused sediments was similar to that in suspended (unperfused) sediments. Substrate affinity (K-m) was higher in the su spended sediments. V-max and K-m both increased when the perfusion rat e was raised, although naturally-low substrate concentrations could me an that variability in perfusion rates has little effect on enzyme act ivity in the field. V-max was uninfluenced by whether ground or stream water was perfused through the sediments, but K-m was higher in cores perfused with groundwater. Increasing concentrations of glucose in th e perfusion water resulted in a progressive inhibition of beta-glucosi dase activity. Although natural concentrations of glucose were low, th e high turnover of enzymatically-released glucose probably means that beta-glucosidase activity could be regulated by product concentration.