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Irreversible inactivation of the membrane-bound enzyme IIlac of the lactose phosphotransferase system of Staphylococcus aureus by triton X-100 and protection by substrates
Authors:Mark L Sussman  John B Hays
Institution:Department of Chemistry, University of Maryland, Baltimore County, Catonsville, Md. 21228, U.S.A.
Abstract:Enzyme IIlac, the membrane-bound component of the lactose phosphotransferase system of Staphylococcus aureus, catalyzes the phosphorylation-transport reaction below:
/></figure> (The sugar can be lactose or one of its analogs.) The effects of the non-ionic detergents Triton X-100, Brij 35, and Tween 40 on the activity of Enzyme II<sup>lac</sup> were studied. Especially striking effects were observed using Triton X-100, a detergent previously used to solubilize and isolate this enzyme. A systematic study of Triton effects over a range of concentrations and temperatures demonstrated three aspects of Triton-membrane interaction. At 0.1% Triton and 25° C Enzyme II<sup>lac</sup> is activated, but remains particulate. At 0.5% Triton and 25° C, it is almost completely solubilized, with good retention of activity. At 0.5% Triton and 37° C, it is rapidly and irreversibly inactivated. Sugar substrates and inhibitory sugar analogs protect Enzyme II<sup>lac</sup> against inactivation; the effect is specific for β-galactosides. The other substrates of Enzyme II<sup>lac</sup>, phospho-Factor III<sup>lac</sup>, does not affect Triton inactivation, and the product analog galactose 6-phosphate slightly enhances the inactivation rate.</td>
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Keywords:To whom correspondence should be addressed  
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