Alkaline phosphatase inhibition cyanide

Alkaline phosphatases [AP, orthophosphoric-monoester phosphorylase (alkaline optimum) EC 3.1.3.1] represent a large family of almost ubiquitous isoenzymes found in organisms from bacteria to animals. In mammals, there are two forms of AP, one form present in a variety of tissues and another form found only in the intestines. They share common attributes in that the phosphatase activity is optimal at pH 8-10, is activated by the presence of divalent cations, and is inhibited by cysteine, cyanides, arsenate, various metal chelators, and phosphate ions. Most conjugates created with AP utilize the form isolated from calf intestine. 

Studies on the cyanide inhibition of the enzyme by Cloetens (C12) and Drill and Riggs (D22) point to the presence of two alkaline phosphatases in animal tissues. We have found cyanide inhibition of intestinal alkaline phosphatase (S19) to be noncompetitive. 

Alkaline phosphatase exists in two forms in animal tissues, one activated by added Mg(II) or Mn(II) and not inhibited by F or CN ions, the other independent of added divalent ions but inhibitable by cyanide . Yeast phosphatase, active at neutral pH, is activated by divalent metal ions in the order Mg > Mn > Ni, Co, Fe ". Metal analysis of purified kidney phosphatase reveals a mixture of bound ions Zn, Cu, Mn, Mg, and Fe . This variety of responses illustrates a classical problem in studies of enzyme activation by metal ions defining the species that is of greatest importance in vivo. 

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