Surficial sediments were collected using a multi-corer.
Five substrates linked to a 7-amido-4-methyl coumarin (MCA) fluorophore, one amino acid – leucine – and four oligopeptides – the chymotrypsin substrates alanine-alanine-phenylalanine (AAF) and alanine-alanine-proline-phenylalanine (AAPF), and the trypsin substrates glutamine-alanine-arginine (QAR) and glutamic acid-gylcine-arginine (EGR) – were used to measure exo- and endo-acting peptidase activities, respectively. Hydrolysis rates of the substrates were measured as an increase in fluorescence as the fluorophore was hydrolyzed from the substrate over time [as in Hoppe, 1993; Obayashi and Suzuki, 2005]. For sediment measurements, peptidase activities were measured in a 1:2 (vol: vol) sediment: autoclaved seawater slurry. 100 micromolar concentrations of substrate were added to triplicate live and single autoclaved killed control incubations. 2 ml of slurry was centrifuged at each timepoint (0, 1h ,2h, and 4 h), filtered, and diluted with 1 ml borate buffer; fluorescence was measured in a 4 ml cuvette. Hydrolysis rates were calculated from the rate of increase of fluorescence in the incubation over time relative to a set of standards of known concentration of fluorophore.
All incubations were conducted at 0 C in the dark.
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