Time course of thermal adaptation in plasma membranes of trout kidney. II. Molecular species composition

lecular species composition of phosphatidylcholine (PC) was determined in plasma membranes of kidney for rainbow trout, Salmo gairdneri, undergoing thermal acclimation between 5 and 20°C. Species of PC from 5”C-acclimated trout were char-acterized by significantly higher values of unsaturation ratio (8.78 vs. 3.15), unsaturation index (2.32 vs. 1.84), and average chain length (34.18 vs. 33.12 carbons) than those of 2O”C-acclimated trout, primarily because of elevated proportions of 16:0/20:4 (8.67 vs. 4.42%) and 16:0/22:6 (15.61 vs. 7.18%) and reduced levels of 14:0/16:0 (3.34 vs. 12.41%). Proportions of saturated and monoenoic species responded most rapidly (within 16-48 h) to temperature change, whereas species con-taining long-chain, polyunsaturated fatty acids increased only after lo-21 days of cold acclimation. The combined results of the present and preceding paper [Hazel and Landrey, Am. J