Chemical modification of milk xanthine oxidase with different modifiers

Xanthine oxidase (XO), purified from buttermilk was subjected to modification with N-phenylmaleimide, p-toluene-sulfonyl chloride, and 2-mercaptobenzimidazole. Spectrophotometric monitoring of the enzyme before and after treatment with these modifiers are presented. The results show that the interaction of XO with the modifiers was accompained by a change in UV absorption, as compared with untreated enzyme. The data indicate that these modifiers caused conformational changes in the polypeptide chain of milk XO due to interaction of these modifiers with sulfahydryl and/or hydroxyl groups. Moreover, the modifiers induce uptake inhibition of milk XO and appeared to be dependant upon either the concentration or incubation time.