The enzymic cleavage of aromatic ethers.

nuclei or mitochondria had no inhibitory action on the guinea-pig microsomal preparation, and guinea-pig nuclei or mitochondria depressed the activity in a rabbit-liver microsomal preparation. Similar inhibitory effects were observed with mouse, dog and rat nuclei or mitochondria. When the nuclei or mitochondria of the guinea pig were heated at 1000 for 2 min. before addition to the combined microsomal and soluble fractions, no inhibition of activity was found. These observations suggested the presence in the nuclei and mitochondria of the guinea pig, mouse, rat and dog livers of heat-labile factors which inhibit the enzymic cleavage of p- ethoxyacetanilide.