Extracellular proteolytic enzyme activity in sediments of an intertidal mudflat

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Abstract
Extracellular proteolytic activity (EPA) on an intertidal mudflat was examined over a 2‐yr period, with focus on characteristics of enzyme systems and the controlling influences on enzyme activity levels. EPA was primarily associated with the particulate rather than the pore‐water phase. Inhibitor studies indicated the presence of primarily metallo‐ and thiol proteases, with pH optima in the range 8–9.5. Temperature optima increased with depth in the sediment, being in the 20°–35°C range for surficial sediments and the 40°–50°C range in the subsurface. Activation energies at environmental temperatures were in the 63–67 kJ mol−1 range. The hypothesis of progressive humification of enzyme activity with depth was discarded on the basis of results from thermal denaturation experiments. EPA levels decreased with depth and hence correlated with substrate concentration and bacterial populations, but this correlation was not a tight one. Seasonal variations in EPA varied with the temperature cycle consistent with, though somewhat damped relative to, the temperature dependence of the enzymes themselves and showed no response to variations in substrate concentrations or bacterial numbers.