Document Detail


Evidence for two distinct lysophospholipase activities that degrade lysophosphatidylcholine and lysophosphatidic acid in neuronal nuclei of cerebral cortex.
MedLine Citation:
PMID:  10320808     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Neuronal nuclei were isolated from immature rabbit cerebral cortex and nuclear lysophospholipase activities studied using two different 1-acyl lysophospholipids: lysophosphatidylcholine (lysoPC) and lysophosphatidic acid (lysoPA). Our interest in these two lysolipids arose from the observation that lysoPA could promote the acetylation of lysoPC by substantially inhibiting a very active nuclear lysoPC lysophospholipase activity, in a competitive manner (R.R. Baker, H. -y. Chang, Mol. Cell. Biochem. (1999) in press). As there was also evidence for nuclear lysoPA deacylation, it was of interest to see whether one activity could possibly utilize both lysolipid substrates. We now have evidence for two separate lysophospholipase activities in neuronal nuclei. The lysoPC lysophospholipase activity was the more active, more highly enriched in the neuronal nuclei, and showed optimal activity at pH 8.4-9, while the lysoPA lysophospholipase activity was maintained over a much broader pH range. The lysoPC activity was substantially inhibited by free fatty acid, and showed considerable stimulation by serum albumin, while the activity utilizing lysoPA was much less affected by these agents. When lysoPC was added to incubations containing radioactive lysoPA, there was no significant inhibition found in rates of release of radioactive fatty acid, indicating that the lysoPA lysophospholipase activity did not utilize the lysoPC substrate. In incubations with lysoPC, MgATP and CoA brought about a sizable formation of phosphatidylcholine whose radioactivity was equally distributed between the sn-1 and sn-2 positions suggesting labelling both directly from the lysoPC substrate and from fatty acid produced by the lysophospholipase activity. By comparison, with the radioactive lysoPA substrate, MgATP and CoA promoted relatively lower levels of phosphatidic acid formation whose principal labelling came directly from the radioactive lysoPA. Largely because of the high activity of the nuclear lysoPC lysophospholipase, there is considerable potential in the neuronal nucleus to limit the use of lysoPC in other reactions, such as the formation of acylPAF (1-acyl analogue of platelet activating factor). It is of interest that conditions associated with brain ischaemia such as increased free fatty acid levels, falling pH and declines in MgATP may allow a preservation of neuronal nuclear lysoPC levels for acetylation. The existence of a separate lysophospholipase activity for lysoPA allows an independent control of lysoPA which can serve as an important regulator of the nuclear lysoPC lysophospholipase.
Authors:
R R Baker; H Y Chang
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  1438     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  1999 May 
Date Detail:
Created Date:  1999-06-17     Completed Date:  1999-06-17     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  NETHERLANDS    
Other Details:
Languages:  eng     Pagination:  253-63     Citation Subset:  IM    
Affiliation:
Department of Biochemistry, Room 5202, Medical Sciences Bldg., University of Toronto, Toronto, Ont. M5S 1A8, Canada.
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MeSH Terms
Descriptor/Qualifier:
Adenosine Triphosphate / pharmacology
Animals
Cell Nucleus / enzymology
Cells, Cultured
Cerebral Cortex / enzymology*
Fatty Acids, Nonesterified / pharmacology
Hydrogen-Ion Concentration
Lysophosphatidylcholines / metabolism*,  pharmacology
Lysophospholipase / antagonists & inhibitors,  metabolism*
Lysophospholipids / metabolism*,  pharmacology
Neurons / metabolism
Rabbits
Serum Albumin, Bovine / pharmacology
Chemical
Reg. No./Substance:
0/Fatty Acids, Nonesterified; 0/Lysophosphatidylcholines; 0/Lysophospholipids; 0/Serum Albumin, Bovine; 56-65-5/Adenosine Triphosphate; EC 3.1.1.5/Lysophospholipase

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