Abstract
Seasonal changes in Leucine-aminopeptidase activity in surface layers of anoxic sediment rich in organic matter were studied from July to October 1997 in a eutrophic lake. The mean bacterial density varied between, 119 ± 20.10 9 cells/g DS with a biomass of 14 ± 3 mgC/g DS. The average Leucine-aminopeptidase activity was 487 ± 177 nmole h -1 g -1 DS over the entire sampling period. It consisted almost entirely of serine and cysteine proteases which had a pH optimum between 8 and 9 and an optimal temperature between 20 °C and 40 °C. In order to study which factors determine this activity, the inputs of organic matter from the trophogenic zone and the concentrations of dissolved proteins and carbohydrates in the sediment were measured. The Leucine-aminopeptidase activity seemed to be repressed by organic matter (OM) flow (r = -0.575, P<0.05) and by carbohydrates (r = -0.684, P<0.05), and induced by dissolved proteins (r = 0.633, P<0.01) throughout the study period.
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