Resistance to Levamisole (R12456) in heat-stable alkaline phosphatases

The inhibitory effect of Levamisole (R12456) on human alkaline phosphatases has been studied. At a concentration of 0.1 mM it is possible to differentiate the source of the enzyme. Enzyme activity relatively resistant to Levamisole (less than 20 percent loss) is present in serum with the Regan isoenzyme, in placental extracts, in the intestinal "B" preparation and in heat-stable alkaline phosphatases "unmasked" after treatment at high ionic strength.