Seasonal variation in kinetic parameters of alkaline phosphatase activity in a shallow Chinese freshwater lake (Donghu Lake)

Seasonal variation of the kinetic parameters of total alkaline phosphatase activity (APA) was studied in a shallow Chinese freshwater lake (Donghu Lake). At the three experimental stations, the values of Vmax of APA were higher and the negative correlation between orthophosphate and the total APA specific activity (Vmax/Chl.) was stronger during summer (from June to September) P depletion. At the same time, the values of Michaelis constant (Km) of APA at the three stations decreased. Phytoplankton seem to compensate for their phosphorus deficiency not only by an increase in enzyme production but also by an improved ability to use low substrate concentrations.