アイテム詳細

要旨

β-glucosidase activity was investigated in stream-bed sediments using 4-methylumbelliferyl-β-D-glucopyranoside (MUF-β-Glc) as a model substrate. In a perfused core technique, water containing MUF-β-Glc was perfused up through sediment cores. β-glucosidase activity was quantified from the release of fluorescent MUF in water discharged from the cores. At low rates of perfusion, maximum β-glucosidase activity (V_max) in perfused sediments was similar to that in suspended (unperfused) sediments. Substrate affinity (K_m) was higher in the suspended sediments. V_max and K_m both increased when the perfusion rate was raised, although naturally-low substrate concentrations could mean that variability in perfusion rates has little effect on enzyme activity 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 the perfusion water resulted in a progressive inhibition of β-glucosidase activity. Although natural concentrations of glucose were low, the high turnover of enzymatically-released glucose probably means that β-glucosidase activity could be regulated by product concentration.