A Repressible Alkaline Phosphatase in Neurospora crassa

The discovery was made that an orthophosphate-repressible alkaline phosphatase exists in Neurospora crassa . Variable phosphate levels in the culture medium caused the enzyme to vary in the order of 100-fold in its range of specific activities. The properties of this 20-fold purified enzyme clearly differentiated it from the alkaline phosphomonoesterase of N. crassa , a P i -repressible alkaline phosphomonoesterase in Escherichia coli , and the alkaline phosphatase of yeast. The enzyme is a nonspecific phosphohydrolase with a pH optimum of 9.0 to 9.5 that cleaves many phosphomonoesters and also pyrophosphate. It is stimulated by ethylenediaminetetraacetate and unaffected by a number of metallic ions tested in the absence of ethylenediaminetetraacetate. The enzyme is stable in the pH range between 7 and 8 but loses activity rapidly at pH 9.0. This loss of activity at pH 9.0 is retarded by phosphate esters serving as substrates, by certain metallic ions, and by P i . The presence of both a repressible and a P i -nonrepressible alkaline phosphoesterase in N. crassa represents a finding not generally observed in other species.