Alkaline phosphatase (ALP) is an extracellular enzyme enabling utilisation of phosphomonoesters as the source of inorganic phosphate (Pi) required for the maintenance of cellular metabolism. Its catalytic properties have been extensively studied in aquatic environments in an attempt to describe its influence on phosphorous cycling in natural waters. Despite its significance and frequent determination, no standard method has been developed so far. In order to examine the effect of various reaction conditions on the kinetic properties of ALP in seawater, the stability of ALP in chloroform-stabilised samples has been studied in addition to the influence of the buffer type, its concentration and pH, the metal-ion content, Pi and incubation time. It might be concluded that the kinetic properties of ALP are significantly influenced by the buffer pH, the concentration of Mg2+ and Zn2+ ions and the incubation period, requiring a precise definition of these reaction parameters in determining a standard method for the measurement of ALP activity in water media
