Oxidation of lysozyme by iodine: isolation of an inactive product and its conversion to an oxindolealanine-lysozyme

Reaction of lysozyme with a half-molar amount of iodine at pH 5.5 gives, in 50% yield (based on iodine), an enzymatically-inactive singly-oxidized derivative. This intermediate can be converted to an oxindole-lysozyme. Analysis showed no modification other than two-electron oxidation of one tryptophan. Substrate analogs prevent the oxidative inactivation. Reaction of crystalline lysozyme with iodine gives the same inactive product found in solution.