Inactivation of Glucose Oxidase by the Cationic Detergent, Hexadecyltrimethylammonium Bromide

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Glucose oxidase (EC 1.1.3.4) was inactivated almost completely at pH 7.0 (0.1 M sodium phosphate buffer, ionic strength = 0.22) by the cationic detergent, hexadecyltrimethylammonium bromide at a molar ratio of HTAB/GOD ?? 1, 700. This inactivation was accompanied by 1) a blue shift in the region of 270-300nm, 2) an increase in FADfluorescence at 520nm, and 3) an approximately 3-fold increase in tryptophan fluorescence at 340 nm. The extent of inactivation of glucose oxidase by the cationic detergent was different from that observed with other detergents under the sameexperimental conditions. Whenthe substrate, D-glucose, was added to the enzyme solution before the addition of hexadecyltrimethylammoniumbromideunder anaerobic conditions, the activity of glucose oxidase decreased to 70% of its original value after incubation at 25°C for 24 hr. In contrast, an anionic detergent, sodium dodecylsulfate, or a nonionic detergent, Triton X- 100, did not produce measurable changes in the enzyme activity. Thus, the inactivation of glucose oxidase by the cationic detergent is caused by the formation of an ion-pair between a cationic head group of the detergent and anionic amino acid residues of the enzyme.
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