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Abstract
1. The rise in p-nitroanisole O-demethylase activity in liver microsomes after phenobarbital treatment of rats slightly preceded, and was greater than, the increase in hepatic microsomal UDP-glucuronyltransferase activity.
2. Predigestion of hepatic microsomes with trypsin was necessary in order to detect the increase in UDP-glucuronyltransferase activity. Digitonin was not able to reveal the increase induced by phenobarbital.
3. Trypsin digestion of hepatic microsomes solubilized about 30% of the proteins in control rats and 45% in microsomes isolated from phenobarbital-treated rats. The amount of solubilized phospholipids was only about 6% in both cases.
4. The proteins solubilized by trypsin contained some components of the mixed-function oxidase including all of the NADPH cytochrome c reductase and a part of the cytochrome P-450 (as cytochrome P-420).
5. The trypsin digestion appears to peel off the superficial proteins of the microsomal vesicle and to uncover UDP-glucuronyltransferase from the deep layers of the microsomal membrane.