Abstract
The cholic acid CoA ligase activity of rat liver was quantitatively inactivated by proteolysis with pronase, chymotrypsin, subtilisin, or proteinase K in intact microsomal vesicles. Under the conditions employed, less than 14% of the lumenal mannose-6-phosphate phosphatase activity was lost, and the mannose-6-phosphate phosphatase activity remained highly latent. After microsomal integrity was disrupted with sodium deoxycholate, protease treatment resulted in a loss of greater than 74% of the mannose-6-phosphate phosphatase activity. Cholic acid CoA ligase activity was unaffected by preincubation of microsomes with sodium taurocholate under conditions that led to the complete expression of latent mannose-6-phosphate phosphatase activity. The data suggest that cholic acid CoA ligase activity is located on the cytoplasmic surface of hepatic microsomal vesicles.
Highlights
The cholic acid CoA ligase activity of rat liver was quantitatively inactivated by proteolysis with pronase, chymotrypsin, subtilisin, or proteinase K in intact microsomal vesicles
The treatment of intact microsomal vesicleswith chymotrypsin,pronase, subtilisin, or proteinase K (Table 1)resulted in the total inactivation of thecholic acid CoA ligase activity when less than 14% of the lumenalmannose-6-Pphosphatase activity was lost
Mannose-6-P phosphatase activity was susceptible to proteolysis afterdisruption of microsomal vesicles with sodiumdeoxycholate or sodiumtaurocholate, (Table l), or by nitrogen cavitation
Summary
The cholic acid CoA ligase activity of rat liver was quantitatively inactivated by proteolysis with pronase, chymotrypsin, subtilisin, or proteinase K in intact microsomal vesicles. Cholic acid CoAligase activity was unaffected by preincubation of microsomes with sodium taurocholate under conditions that led to the complete expression of latent mannose-6-phosphate phosphatase activity. The data suggest that cholic acid CoA ligase activity is located on the cytoplasmic surface of hepatic microsomal vesicles. P-450, wereasymmetrically localized to either thceytoplasmic or the lumenal surface [5].Glucose-6-phosphate phosphatase, associated withall hepatic microsomal vesicles [7, 8], has been demonstrated to be located exclusively onthelumenalsurface by proteolysis experiments and by product localization [5,7,8]. Mannose-6-P phosphatase activity is highly latent.' The latency of mannose-6-Pphosphatase activity appears to provide a reliable index of microsomal integrity [9]
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