Prednisolone enhances aminopeptidase turnover in adult rat small intestine |
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Authors: | James Scott Mervyn Maze Timothy J Peters |
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Institution: | 1. Department of Medicine, Royal Postgraduate Medical School, London, W12 0HS, UK;2. MRC Clinical Research Centre, Harrow, Middlesex, HA1 3UT, U.K. |
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Abstract: | In adult male rats, fed prednisolone (0.75 mg/kg/day) for 7 days, brush border aminopeptidase activity was increased (P < 0.001) by 106% compared to pair-fed controls. 14C]Tyrosine was injected intraperitoneally 16 h and 3H]tyrosine 6 h before death. The 3H/14C ratio was 1.79 ± 0.21 (S.D.) in purified microvillus membranes from treated rats compared to 1.30 ± 0.16 (P < 0.01) in controls. Polyacrylamide gel electrophoresis of brush border membranes under denaturing conditions showed that the increased double-isotope ratio in membranes from treated rats was mainly in the high molecular weight protein subunits (> 80 kDa) Detergent-solubilized aminopeptidase was purified after in vivo labeling by protein A-Sepharose-antiaminopeptidase affinity chromatography. The 3H/14C ratio in aminopeptidase was 2.42 ± 0.15 (P < 0.05) in treated rats compared to 1.63 ± 0.13 in controls. Over the experimental period steady-state isotope reutilization and protein labeling was demonstrated and there was no isotope metabolism. Total microvillus membrane lipid content was unaffected by prednisolone. We conclude that prednisolone increases brush border aminopeptidase activity by increasing enzyme turnover. Other high molecular weight brush border proteins were similarly affected. |
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Keywords: | Aminopeptidase Prednisolone Protein turnover (Rat intestine) |
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