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Protein degradation in extracts of exponential and stationary phase Vibrio cells
Abstract:
The degradation of the foreign protein [14C]methyl apohaemoglobin ([14C-me]globin) was stimulated by ATP in cell-free extracts from exponential phase and shaken and standing stationary phase Vibrio cells. A marked stimulation by ATP of the degradation of [14C-me]globin was observed with exponential phase cell extracts which were preincubated for 30 min at 30 degrees C. Maximum stimulation was obtained with 3 mM-ATP and optimum degradation was at pH 8.0-8.5. Preincubation of extracts from both types of stationary phase cells did not affect the degree of ATP stimulation. The amount of ATP stimulation of [14C-me]globin degradation by exponential phase extracts decreased markedly when the cells were starved in a growth limiting minimal medium before preparation of the cell extracts. In the exponential and both types of stationary phase extracts most of the activity was located in the cytoplasmic fractions. Although the periplasmic preparations contained a minor portion of the total activity, this activity showed a greater percentage stimulation by ATP. In the absence of ATP the specific proteolytic activities of the extracts from exponential and both types of stationary phase cells were similar. The proteolytic activities in all the cell extracts were inhibited to the same extent by phenylmethylsulphonyl fluoride, but the exponential and both types of stationary phase cell extracts were inhibited to different extents by EDTA and p-hydroxymercuribenzoate. The results suggest that the proteolytic systems responsible for the degradation of abnormal proteins are different in exponential and stationary phase Vibrio cells.
Insights
ATP stimulates the breakdown of foreign proteins in Vibrio cells. This protein degradation process differs between exponential and stationary growth phases, indicating distinct proteolytic systems.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Foreign protein degradation is crucial for cellular homeostasis.
- The role of ATP in protein degradation varies across different bacterial growth phases.
- Understanding Vibrio proteolytic systems provides insights into bacterial physiology.
Purpose of the Study:
- To investigate the effect of ATP on foreign protein degradation in Vibrio.
- To compare ATP-stimulated proteolysis in exponential versus stationary phase Vibrio cells.
- To characterize the proteolytic systems involved in abnormal protein turnover.
Main Methods:
- Utilized cell-free extracts from Vibrio cells at different growth phases (exponential, stationary).
- Assessed the degradation of radiolabeled foreign protein ([14C]methyl apohaemoglobin) in the presence and absence of ATP.
- Investigated the impact of preincubation, pH, and nutrient limitation on ATP-stimulated degradation.
- Fractionated cell extracts to localize proteolytic activity (cytoplasmic, periplasmic).
- Examined the effects of protease inhibitors (phenylmethylsulphonyl fluoride, EDTA, p-hydroxymercuribenzoate) on proteolytic activity.
Main Results:
- ATP significantly stimulated the degradation of [14C]methyl apohaemoglobin in exponential phase Vibrio extracts, with optimal activity at pH 8.0-8.5 and 3 mM ATP.
- Preincubation of stationary phase extracts did not enhance ATP stimulation.
- Starvation of exponential phase cells reduced ATP stimulation of proteolysis.
- Proteolytic activity was primarily found in cytoplasmic fractions, with higher percentage stimulation by ATP in periplasmic fractions.
- Protease inhibitor sensitivity varied between exponential and stationary phase extracts, suggesting distinct enzyme compositions.
Conclusions:
- ATP-dependent proteolysis of foreign proteins occurs in Vibrio cells.
- The proteolytic systems responsible for abnormal protein degradation differ between exponential and stationary phases in Vibrio.
- These findings highlight the dynamic nature of bacterial proteolytic machinery in response to growth conditions.