Sera from patients with halothane hepatitis contain immunoglobulin G (IgG) antibodies to trifluoroacetylated liver microsomal proteins of 100, 76, 59, 57 and 54 kDa, which are produced as a consequence of metabolism of halothane to trifluoroacetyl halide by cytochrome(s) P450. In the present study, the membrane topographies of the various antigens in rat liver microsomal fractions were investigated. Liver microsomal fractions from rats treated with halothane in vivo, and rat liver microsomal fractions which had been incubated with halothane in vitro, were used as the source of tri-fluoroacetyl antigens. The antigens were detected by immunoblotting. Whereas the 100, 76, 59 and 57 kDa antigens were solubilized from the microsomal membrane by either 0.1 M sodium carbonate or 0.1% (w/v) sodium deoxycholate, the 54 kDa antigen was not solubilized by 0.1% (w/v) sodium deoxycholate. In intact microsomal fractions, the 100, 76, 59 and 57 kDa antigens were not degraded appreciably by trypsin unless detergent was added to permeabilize the microsomal membrane. These results indicate that the 54 kDa antigen is an integral membrane protein, whereas the 100, 76, 59 and 57 kDa antigens are peripheral membrane proteins situated within the lumen of microsomal vesicles, and hence presumably located within the lumen of the endoplasmic reticulum in vivo.
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