Extracellular Proteolytic Activity in the Surface Sediment of a Eutrophic Inlet.

Abstract

The potential aminopeptidase activity (APA) in surface sediment (0-1 cm), and important ecological factors of a eutrophicated inlet were monitored for one and a half years on a weekly to biweekly basis to elucidate the fluctuations in extracellular hydrolysis of protein during an annual cycle, and main regulating factors on an annual and/or a seasonal basis. APA was estimated in sediment slurry prepared with unamended bottom water, as the Vmax of the rate of the enzymatic hydrolysis of a coumarine derivative fluorophore at in situ temperatures. APA varied 5-6 fold during the study period with highest values (225-275 nmole AMC h-1 g-1 dry weight) during September-October or early June when the temperature was 22-28°C and dissolved oxygen concentrations (DO) (2-4 mg L-1) in overlying bottom water were high, and much lower values (ca. 50 nmoles AMC h-1 g -1 dry weight) in July-August or December-February. On an annual basis, APA correlated only marginally (p > 0.05; r = 0.25) with the protein content of the surface sediment and not at all with any other variables. However, it showed highly significant correlations (p > 0.001) with temperature (r = 0.81), and protein content (0.65) in mid December-early June, when temperatures were relatively low (ca. 12-22°C) and DO was abundant (ca. 2-6 mg L-1) in overlying bottom water.