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Binding of ATP citrate lyase to the microsomal fraction of rat liver
Abstract:
Purified rat liver ATP citrate lyase is shown to bind to the microsomal fraction of rat liver. Under the same conditions the enzyme does not bind significantly to the mitochondrial fraction or to the outer membrane prepared from the mitochondrial fraction. The binding component of the microsomal fraction is further identified as the endoplasmic reticulum, and a protein component of the membrane is involved in binding. Binding decreases with increasing salt concentration. It requires more than 50 mM potassium phosphate or 60 mM potassium chloride to decrease binding significantly whereas complete inhibition of binding is observed in the presence of 0.01 mM CoA. The binding capacity of the microsomal fraction is shown to be high enough to allow most, if not all, the ATP citrate lyase present in rat liver to be bound to the microsomal fraction even when the enzyme has been induced over 10-fold by dietary manipulations. No significant difference has been found when comparing the binding of the phospho and dephospho forms of ATP citrate lyase.
Insights
Rat liver ATP citrate lyase (ACL) binds to the endoplasmic reticulum, not mitochondria. This binding is sensitive to salt and CoA concentration, indicating its physiological relevance in cellular processes.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- ATP citrate lyase (ACL) is a key enzyme in lipogenesis and cholesterol synthesis.
- Understanding the localization and regulation of ACL is crucial for metabolic research.
Purpose of the Study:
- To investigate the binding characteristics of purified rat liver ATP citrate lyase (ACL).
- To identify the specific cellular fractions and components involved in ACL binding.
- To determine the influence of various conditions on ACL binding.
Main Methods:
- Enzyme purification and binding assays using rat liver fractions (microsomes, mitochondria).
- Fractionation of mitochondria to isolate outer membrane.
- Varying salt concentrations (potassium phosphate, potassium chloride) and CoA levels to assess binding inhibition.
- Dietary manipulation to induce ACL expression.
Main Results:
- Purified rat liver ACL binds to the microsomal fraction, specifically the endoplasmic reticulum.
- No significant binding was observed with mitochondrial fractions or outer mitochondrial membranes.
- Binding is dependent on salt concentration and strongly inhibited by CoA.
- The endoplasmic reticulum has sufficient binding capacity for total liver ACL, even after induction.
- Phospho and dephospho forms of ACL showed no difference in binding.
Conclusions:
- Rat liver ATP citrate lyase (ACL) predominantly binds to the endoplasmic reticulum.
- The binding is regulated by salt and CoA, suggesting physiological control mechanisms.
- ACL localization to the endoplasmic reticulum is robust and can accommodate enzyme level changes.