The iodine inactivation reaction of Bacillus cereus 569/H penicillinase (penicillin amido-β-lactam hydrolase, EC 126.96.36.199) was studied. At pH 9 a 30-35% decrease in enzyme activity was observed. The reaction was found to be complex, its first step being a conformational change which brought the tyrosine and tryptophan side chains buried in native proteins to the surface of the molecule. This was followed by the oxidation of one tryptophan molecule and subsequent stabilization of the conformational change which occurred in the alkaline medium. Decrease of enzyme activity ensued when one molecule of tyrosine was substituted by iodine giving rise, in alkaline medium, to diiodotyrosine and, in acidic medium with the enzyme oxidized, to monoiodotyrosine.
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