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Effect of bacterial endotoxin and inhibitors on tryptophan oxygenase induction in mouse liver slices
Abstract:
Tryptophan oxygenase activity in mouse liver slices maintained in cluture medium, in Krebs-Ringer bicarbonate solution, or in homologous whole blood declined within 3 hr to about one-half the original level. Actinomycin D and puromycin accelerated the rate of decline, but endotoxin did not. Direct addition of tryptophan to the medium resulted in a higher than normal tryptophan oxygenase activity within 1 hr, and this was maintained well above that of control liver slices up to 6 hr. Triamcinolone, at a dose that doubles tryptophan oxygenase activity in vivo, had no effect on the enzyme in liver slices. Actinomycin and endotoxin did not alter the substrate induction of tryptophan oxygenase; however, puromycin did, but to a limited extent. Liver slices prepared from mice 4 hr after an injection of cortisone had a greater tryptophan oxygenase activity than those of controls. Either endotoxin or actinomycin D resulted in a more rapid decline of the enzyme when added to the slices than was observed in the controls.
Insights
Tryptophan oxygenase activity in mouse liver slices decreases rapidly. Tryptophan addition boosts activity, while certain inhibitors affect enzyme levels differently.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- Tryptophan oxygenase (TO) is a key enzyme in tryptophan metabolism.
- Understanding TO regulation is crucial for metabolic studies.
Purpose of the Study:
- To investigate the stability and regulation of tryptophan oxygenase in mouse liver slices.
- To examine the effects of substrate, inhibitors, and hormones on TO activity in vitro.
Main Methods:
- Incubation of mouse liver slices in various media (culture medium, Krebs-Ringer solution, whole blood).
- Treatment with tryptophan, actinomycin D, puromycin, endotoxin, triamcinolone, and cortisone.
- Measurement of tryptophan oxygenase activity over time.
Main Results:
- Tryptophan oxygenase activity declined significantly in liver slices within 3 hours.
- Actinomycin D and puromycin accelerated the decline, while endotoxin had no effect.
- Tryptophan addition increased TO activity, an effect not observed with triamcinolone in vitro.
- Cortisone treatment in vivo increased TO activity in subsequently prepared liver slices.
Conclusions:
- Mouse liver slice preparations show rapid loss of tryptophan oxygenase activity.
- Substrate availability (tryptophan) is a key factor in maintaining TO activity in vitro.
- Differential effects of inhibitors suggest complex post-transcriptional regulation mechanisms.