Substrate specificities and properties of human phospholipases A2 in a mixed vesicle model
Studies of the specificity of phospholipases A2 (PLA2s) for different substrates have usually been carried out in vesicles or mixed micelles, where differences in shape, size, or charge of vesicles formed with different phospholipids may give misleading results. Another factor is binding of the enzy...
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Published in: | The Journal of biological chemistry 1992-09, Vol.267 (26), p.18342-18348 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Subjects: | |
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Online Access: | Get full text |
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Summary: | Studies of the specificity of phospholipases A2 (PLA2s) for different substrates have usually been carried out in vesicles
or mixed micelles, where differences in shape, size, or charge of vesicles formed with different phospholipids may give misleading
results. Another factor is binding of the enzyme to the phospholipid surface, which has recently been addressed using vesicles
of an anionic phospholipid, dimyristoyl-sn-glycero-3-phosphomethanol (DMPM) to which some extracellular PLA2s were shown to
bind with a very high affinity (Jain, M. K., and Berg, O. G. (1989) Biochem. Biophys. Acta 1002, 127-156). In the present
report we have used a similar system to study the substrate preferences of two human PLA2s that are thought to be physiologically
relevant in the metabolism of arachidonic acid: a recombinant form of the human synovial fluid (14 kDa) PLA2 and the cytosolic
(85 kDa) PLA2 found in monocytic cells. It is shown that both human enzymes bind tightly to DMPM vesicles and follow the basic
characteristics of processive hydrolysis in this model using analysis of progress curves and substrate competition experiments.
Mixed vesicles containing DMPM with small amounts (3-5 mol%) of other phospholipids have been used to study the substrate
selectivity of the two human isoenzymes. The synovial fluid PLA2 shows a clear preference (approximately 7-fold) for sn-glycero-3-phosphoethanolamine
over sn-glycero-3-phosphocholine. Within glycerophosphocholines, this enzyme displays little preference for the sn-2 fatty
acyl group, and a slight preference for phospholipids with sn-1-acyl versus sn-1-alkyl substituents. In contrast, the cytosolic
PLA2 shows a marked selectivity for arachidonoyl in the sn-2 position and only minor differences in selectivity for the polar
head group in the sn-3 position. This enzyme does not distinguish between sn-1-acyl and sn-1-alkyl subclasses of glycerophosphocholines. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1016/s0021-9258(19)36966-2 |