AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 6 923-R928, Copyright © 1988 by American Physiological Society
Acylation of lysophosphatidylcholine in liver microsomes of thermally acclimated trout
R. C. Livermore and J. R. Hazel
Department of Zoology, Arizona State University, Tempe 85287.
The specificity of acyl-coenzyme A (CoA): lysophosphatidylcholine
acyltransferase (LPCAT; EC 2.3.1.23) was determined for a range for
acyl-CoA substrates differing with respect to chain length and degree of
unsaturation in liver microsomes of thermally acclimated (5 and 20 degrees
C) rainbow trout, Salmo gairdneri. Absolute levels of oleate incorporation
into phosphatidylcholine (PC) were determined at substrate concentrations
in the physiological range (12 microM) and higher (64 microM). The
specificity of LPCAT was determined by the extent to which competing
substrates decreased the incorporation of oleate. LPCAT specificity was
significantly influenced by both assay and acclimation temperature at total
substrate concentrations of both 72 and 256 microM. A clear preference for
14- and 16-carbon monoenes was exhibited by LPCAT from 20 but not 5 degrees
C-acclimated trout. Furthermore, LPCAT from 5 degrees C-acclimated trout
preferentially incorporated long chain and polyunsaturated fatty acids
(eicosadienoyl, arachidonoyl, erucoyl) and excluded 18-carbon unsaturates
at an assay temperature of 5 degrees C compared with 20 degrees C; at 20
degrees C, 18-carbon unsaturates were incorporated more readily than
20-carbon species. Linolenic acid (18:3N3) was generally excluded from
incorporation, reflecting a possible mechanism by which this precursor of
docasahexaenoic acid (22:6N3, n - 3) remains available for modification.
These results indicate that trout liver LPCAT preferentially incorporates
fatty acids into PC on the basis of both chain length and degree of
unsaturation in a manner consistent with the temperature-induced
restructuring of membrane phospholipids.
