Interaction of CetyltrimethylammoniumBromide andIts Gemini Homologue Bis(cetyldimethylammonium)butane Dibromide withXanthine Oxidase.

The interaction of xanthine oxidase (XO), a key enzymein purinemetabolism, with cetyltrimethylammonium bromide (CTAB) and bis(cetyldimethylammonium)butanedibromide (C16C4C16Br2) has been studied using tensiometry, spectrofluorometry, spectrophotometry,and circular dichroism at pH 7.4 and 25 °C. The tensiometricprofiles of CTAB and C16C4C16Br2in the presence of XO exhibit a single break at a lower surfactantconcentration termed as C1compared to their CMC in thebuffered solution and show the existence of interaction between thesurfactants and the enzyme. The results of the multitechnique approachshowed that, although both CTAB as well as C16C4C16Br2interact with the XO, C16C4C16Br2interacts more stronglythan its conventional single chain counterpart. Fluorescence and absorptionmeasurements revealed that, compared to CTAB, C16C4C16Br2is more effective in unfoldingthe enzyme. Change in XO activity by the surfactants was in concurrencewith the structural alterations monitored by circular dichroism andshowed structural stabilization of XO at higher surfactant concentrations,consistent with the aggregation results. This stabilization has beenexplained in light of strong tendency of C16C4C16Br2for micellar growth and membrane/waterstabilization of proteins by membrane-like fragments provided by higherconcentrations of C16C4C16Br2. The results are related to the stronger electrostatic andhydrophobic forces in C16C4C16Br2, owing to the presence of two charged headgroups and twohydrophobic tails. [ABSTRACT FROM AUTHOR]