Role of sea water DIP and DOP in controlling bulk alkaline phosphatase activity in N.W. Mediterranean Sea (Toulon, France)

The regulation of alkaline phosphatase activity by dissolved inorganic (DIP) and organic phosphorus (DOP) and the contribution of DOP as phosphorus source were studied monthly in Toulon Bay (NW Mediterranean, France) in 2005–2006. The concentrations of DIP and DOP varied respectively from 0 to 0.185 μM and from 0 to 0.329 μM. The bulk activities (Vm, Km, Vm/Km) were measured using MUFP as substrate. Its high affinity component (Km: 0.05–1.00 μM) was negatively correlated with the sum of the concentrations of DIP and DOP but not with these compounds taken independently. A negative correlation with DIP was found when the concentrations of DOP were lower than 0.08 μM. A negative correlation with DOP was shown when the concentrations of DIP were lower than 0.05 μM. This high affinity component can be considered as a valuable indicator for the potential utilization of the compounds which contribute to the intracellular phosphorus pool.