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Translocation to rat liver mitochondria of phosphatidate phosphohydrolase
1Department of Biochemistry, University of Nottingham Medical School, Queens Medical Centre, U.K.
Abstract:
When a particle-free supernatant fraction from rat liver was incubated at 37 degrees C with mitochondria and oleate, some of the enzyme phosphatidate phosphohydrolase (PAP), initially present in the particle-free supernatant, was recovered, after the incubation, bound to mitochondria. This translocation of PAP from cytosol to mitochondria was stimulated by oleate or palmitate in a similar fashion to the stimulation of translocation of PAP to endoplasmic reticulum [Martin-Sanz, Hopewell & Brindley (1984) FEBS Lett. 175, 284-288]. Translocation of PAP from particle-free supernatant to a partially purified mitochondrial-outer-membrane preparation was also stimulated by oleate. More PAP was bound to a mitochondrial-outer-membrane fraction washed in 0.5 M-NaCl before resuspension in sucrose than to a sucrose-washed mitochondrial-outer-membrane preparation. In contrast, washing of microsomal membranes in 0.5 M-NaCl did not enhance the binding of PAP to these membranes. PAP also binds to phosphatidate-loaded mitochondria or microsomes (microsomal fractions). In the experimental system employed, more PAP bound to mitochondria loaded with phosphatidate than to microsomes loaded with phosphatidate. The results are discussed in relation to the role of mitochondrial phosphatidate in liver lipid metabolism.
Insights
Fatty acids like oleate stimulate the enzyme phosphatidate phosphohydrolase (PAP) to move from the cytosol to mitochondria. This liver enzyme translocation is crucial for lipid metabolism.
Area of Science:
- Biochemistry
- Cell Biology
- Liver Metabolism
Background:
- Phosphatidate phosphohydrolase (PAP) is a key enzyme in lipid metabolism.
- The localization and regulation of PAP are critical for understanding cellular lipid pathways.
Purpose of the Study:
- To investigate the translocation of PAP from the cytosol to mitochondria in rat liver cells.
- To determine the role of fatty acids, specifically oleate and palmitate, in stimulating PAP translocation to mitochondria.
Main Methods:
- Incubation of particle-free liver supernatant with rat liver mitochondria and oleate at 37°C.
- Preparation and washing of mitochondrial outer membrane and microsomal fractions.
- Assessing PAP binding to mitochondrial and microsomal fractions under various conditions, including phosphatidate loading.
Main Results:
- Oleate and palmitate significantly stimulated the translocation of PAP from the cytosol to mitochondria.
- Oleate also promoted PAP translocation to a partially purified mitochondrial outer membrane preparation.
- Washing mitochondrial outer membranes with 0.5 M NaCl enhanced PAP binding, unlike microsomal membranes.
- PAP exhibited greater binding to phosphatidate-loaded mitochondria compared to phosphatidate-loaded microsomes.
Conclusions:
- Fatty acids play a regulatory role in the mitochondrial translocation of PAP.
- Mitochondria, particularly when loaded with phosphatidate, serve as a significant binding site for PAP.
- These findings suggest a role for mitochondrial phosphatidate in liver lipid metabolism.