Inactivation of microsomal Ca2+-ATPase by 2-chloroethylethyl sulfide

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Abstract

Exposure of liver microsomes to 2-chloroethylethyl sulfide (CEES) led to a dose-dependent decrease of Ca2+-ATPase activity. Studies on a structural requirement and a time dependence suggest that the enzyme inhibition may proceed via an instantaneous process involving an alkylation by an unstable intermediate, presumably a sulfonium form. It is noteworthy that the microsomal Ca2+-ATPase was more sensitive to CEES than the Na+K+-ATPase from erythrocyte membranes. The Ca2+-ATPase was inhibited non-competitively by CEES, and its inhibitory action was independent of Ca2+ concentrations. The involvement of membrane phospholipid in the enzyme inhibition is excluded, since the temperature dependence of microsomal Ca2+-ATPase was not affected by CEES. Moreover, Triton X-100-solubilized Ca2+-ATPase was inactivated by the compound to the same extent as the membrane-bound enzyme was. Thus, it is suggested that CEES inactivates Ca2+-ATPase by alkylating the enzyme molecule at a region other than the active site.

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