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 loo-fold in its range of spechic activities. The properties of this ZO-fold purified enzyme clearly differentiated it from the alkaline phosphomonoesterase of N. crassa, a Pi-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 Pi. The presence of both a repressible and a Pi-nonrepressible alkaline phosphoesterase in N. crassa represents a finding not generally observed in other species.