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Decrease of rat liver cysteine dioxygenase (cysteine oxidase) activity mediated by glucagon
Abstract:
The hepatic cysteine dioxygenase activity of rats was markedly decreased by the intraperitoneal administration of glucagon. The enzyme activity was also decreased by either dibutyryl cyclic AMP or theophylline. The prior administration of actinomycin D completely blocked the glucagon-mediated decrease of enzyme activity, while administrations of this inhibitor of protein synthesis after glucagon injection did not block the decrease of enzyme activity. A single administration of actinomycin D resulted in a slight increase of cysteine dioxygenase activity in the rat liver. On the other hand, the injection of cycloheximide resulted in a rapid decrease of the hepatic cysteine dioxygenase with a half-life of 2.5 h. The half-life of the enzyme in rat liver after glucagon administration was one hour. The administration of hydrocortisone or insulin had no effect on the glucagon-mediated decrease of cysteine dioxygenase of rat liver. The enzyme activity of alloxan diabetic rat liver was almost the same as that of the intact rat liver. The evidence obtained here suggests that enhancement of degradation or inactivation of cysteine dioxygenase is responsible for the glucagon-mediated decrease of the enzyme activity in rat liver.
Insights
Glucagon reduces rat liver cysteine dioxygenase activity by increasing enzyme degradation. Protein synthesis inhibition before glucagon prevents this decrease, suggesting a role for new protein synthesis in the reduction.
Area of Science:
- Biochemistry
- Enzymology
- Hepatology
Background:
- Cysteine dioxygenase (CDO) is a key enzyme in L-cysteine metabolism.
- Regulation of hepatic CDO activity is crucial for maintaining amino acid homeostasis and cellular redox balance.
Purpose of the Study:
- To investigate the mechanism by which glucagon affects hepatic cysteine dioxygenase activity in rats.
- To determine if the glucagon-mediated decrease in enzyme activity involves changes in protein synthesis or degradation.
Main Methods:
- Administration of glucagon, dibutyryl cyclic AMP, theophylline, actinomycin D, and cycloheximide to rats.
- Measurement of hepatic cysteine dioxygenase activity.
- Determination of enzyme half-life following glucagon administration.
Main Results:
- Glucagon, dibutyryl cyclic AMP, and theophylline decreased hepatic cysteine dioxygenase activity.
- Actinomycin D blocked the glucagon effect when administered prior to glucagon, but not after.
- Cycloheximide induced a rapid decrease in enzyme activity with a half-life of 2.5 hours, while glucagon administration resulted in a half-life of 1 hour.
Conclusions:
- The glucagon-mediated decrease in hepatic cysteine dioxygenase activity is likely due to enhanced degradation or inactivation of the enzyme.
- The results suggest that de novo protein synthesis is not required for the glucagon-induced reduction in enzyme activity.