Alkaline phosphatase inactivation by mixed function oxidation systems.

Alkaline phosphatase is inactivated by mixed function oxidation systems. OH. radicals, generated via an ascorbate-modified Haber-Weiss cycle or a Fenton-type reaction, seem to be responsible for the protein oxidative damage. Experiments with hydroxyl radical scavengers, enzyme substrates, products, and metal cofactors suggest that a "site-specific" radical attack takes place at or near the active center. Vitamin E fails to protect alkaline phosphatase; uric acid, instead, is particularly effective in shielding the protein against covalent modifications.