The action of cyanate on human and pig kidney alkaline phosphatases

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Abstract
1. At concentrations of cyanate up to 0·2m there is an apparently reversible combination with alkaline phosphatase (EC 3.1.3.1), but higher concentrations inhibit alkaline phosphatase irreversibly by a process that is time-dependent. 2. The effect of 0·2m-cyanate on the enzymic reaction velocity depends on the substrate concentration. There is inhibition when the substrate concentration is 1·0mm or higher, but at lower substrate concentrations cyanate has an activating effect. 3. The pH-dependence of the reversible reaction suggests that cyanate may react with a thiol group at or near the active site of the enzyme, preventing a conformational change that is believed to be important in the mechanism of action of alkaline phosphatase. 4. Prolonged treatment with 0·6m-cyanate probably carbamoylates all free amino groups in the enzyme molecule and generates a new enzyme with decreased Vmax. and increased Km.