ENZYMATIC HYDROLYSIS OF THIOESTERS, ESFECIALLY IN RELATION TO O-ESTERASE

1. The occurrence of an enzyme in mammalian liver was as-certained which was capable to hydrolyze lower thioesters.<br> 2. Of various tissues of rats, the liver was found to have the most active enzymatic activity, while the other tissues exerted almost no activity except kidney and blood. On the other hand, acetyl thiocholine was hydrolyzable not by livers, but well by brain-homogenates.<br> 3. From rabbit livers, we obtained the active enzyme preparation by ammonium sulphate fractionation. Although it contained also O-esterase activity, it attacked thioesters much more rapidly than O-esters.<br> 4. Comparing with O-esterase activity, we investigated several enzymatic properties of S-ester hydrolyzing activity of the liver enzyme, that is, pH-activity, pS-activity, temperature-activity, heat-stability and the influences of atoxyl and other inhibitors. These properties of S-esterase activity are well accordant with those of O-esterase activity.<br> 5. On the .basis of these results, there seemed not to exist S-ester specific hydrolyzing enzyme, but O-esterase itself hydrolyzes thioester possibly due to its loose substrate-specificity.<br> 6. We could obtain no experimental evidence for phosphorolysis of these S-esters by our liver enzyme.