The substrate specificity and inhibition of alkaline phosphatases of cow's milk and calf intestinal mucosa

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Abstract
The sub-strate specificity of alkaline phosphatases, purified from cow''s milk and calf intestinal mucosa, was investigated, using a wide range of com-pounds under several different experimental conditions. All true orthophosphate monoesters were rapidly hydrolyzed by both enzymes, as well as the orthophosphoamide, phosphocreatine, and the enolic phosphate, phosphoenolpyruvate. Sodium pyrophosphate, sodium hexa-metaphosphate, diphenyl pyrophosphate, ATP, ADP and DPN were not hydrolyzed by either enzyme, showing absence of any pyrophosphatase activity. Absence of diesterase activity was shown from studies with partially degraded yeast nucleic acid, both in the presence and absence of added ribonuclease. A number of organic polyphosphates, phosphates, phosphites, phosphonates and fluorophosphonates were found to cause only slight inhibition of milk or intestinal phosphatase at 10-2 [image] concentration under the experimental conditions used. However, I2 and cysteine at 10-3 [image] concentration both caused strong inhibition of the 2 phosphatases. A possible mechanism for the inhibition by iodine is discussed.