Surfactin, an acidic lipopeptide of Bacillus subtilis, at 70 mu M non-competitively inhibited alkaline phosphatase without its glycosyl-phosphatidylinositol anchor by 50%. Enzyme activity was restored by adding 50 mu M ZnCl2 and 1 mM MgCl2 confirming the chelating action of the free carboxyl groups of the Asp and Glu residues in the peptide moiety of surfactin.