Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used

Abstract. Ectoenzymatic activity, prokaryotic heterotrophic abundances and production were determined in the Mediterranean Sea. Sampling was carried out sub-surface, deep chlorophyll maximum layer (DCM), core of Levantine intermediate waters deeper part mesopelagic layers. Michaelis–Menten kinetics assessed using a large range concentrations fluorogenic substrates (0.025 to 50 µM). As consequence, Km (Michaelis–Menten half-saturation constant) Vm (maximum hydrolysis velocity) parameters for both low- high-affinity enzymes alkaline phosphatase, aminopeptidase (LAP) β-glucosidase (βGLU). Based on constant derived from high-LAP-affinity enzyme (0.025–1 µM substrate concentration range), situ N proteins contributed 48 % ± 30 bacterial nitrogen demand within epipelagic layers 180 154 upper The LAP rate higher than only when considering enzyme. 10 growth efficiency, cumulative rates C polysaccharides average 2.5 1.3 carbon sampled (sub-surface DCM). This study clearly reveals potential biases current past interpretations kinetic three tested based fluorogenic-substrate used. In particular, / βGLU enzymatic ratios some depth-related trends differed between use high low substrates.