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 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.
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Nyc et al. (1966) studied this question.
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