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Preliminary studies on the significance of alkaline phosphatase activity in the diatom Phaeodactylum tricornutum Bohlin
R. García Ruiz, I. Hernández, J. Lucena and F.X. Niell

Alkaline phosphatase activity (APA) and total cellular phosphorus were investigated in batch culture of the diatom Phaeodactylum tricornutun Bohlin. The alga used three phosphomonoesters as P source: p-nitrophenylphosphate (pNPP), methyl-umbelliferylphophate (MUP) and ß-glycerophosphate. The enzyme exhibited an apparent negative cooperativity for the hydrolysis of pNPP and MUP. Affinity was higher for MUP than for pNPP, but maximum velocity was similar. Incubation at phosphate concentration < 50 µM shows no effect on APA, but the enzymatic activity decreased markedly at higher phosphate concentrations. The decrease depended on the time of incubation (4 days), suggesting repression of enzyme synthesis. In cultures supplied with ß-glycerophosphate the enzyme utilised preferentially this substrate, instead of MUP. Phosphatase activity was inversely related with total phosphorus content. The ability to take up phosphate and APA increased markedly with increased phosphorus deficiency. Maximum APA (27 fg MU cell-1 h-1) was observed when phosphate uptake was high (Vmax=6.5 fm P cell-1 h-1) and phosphorus content was low (0.33 pg P cell-1). In contrast, a minimum APA (1.4 fg MU cell-1 h-1) was associated to low phosphate uptake (less than 1 fm P cell-1 h-1) and maximum phosphorus content (9.6 pg P cell-1).

Contents of this volume Sci. Mar. 61(4) : 517-525 Back PDF
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