MOLECULAR ARCHITECTURE AND BIOPHYSICAL PROPERTIES OF PHOSPHOLIPIDS DURING THERMAL ADAPTATION IN FISH - AN EXPERIMENTAL AND MODEL STUDY

Phospholipids from livers of carps (Cyprinus carpio L.) adapted to win ter (5 degrees C) and summer (25 degrees C) temperatures were isolated , and the fatty acid composition of total phospholipids, as well as mo lecular species composition of diacyl phosphatidylcholines and ethanol amines, were determined. Order parameter of 5-doxyl stearic acid and s teady-state fluorescence anisotropy of different anthroyloxy fatty aci ds-[2-,12(N-9-anthroyloxy)stearic acid and 16(N-9-anthroyloxy)palmitic acid-embedded in native and synthetic (16:0/16:0, 16:0/22:6, 18:0/22: 6, 18:1/22:6, 20:4/20:4, 22:6/22:6 phosphatidylcholines and 16:0/18:1, 18:1/22:6 phosphatidylethanolamines) phospholipid vesicles was also d etermined between -30 and 30 degrees C and 5 and 30 degrees C, respect ively. There is an accumulation of 1-monoenoic, 2-polyenoic diacyl pho sphatidylcholine and ethanolamine with a concomitant reduction of 1-st earoyl,2-docosahexaenoyl species in the cold-adapted state. Despite a 30% accumulation of long-chain polyunsaturated fatty acids in phosphol ipids in cold, there is only a 5 degrees C downshift in the solid-gel to liquid-crystalline phase transition temperature (-8 vs. -13 degrees C). Vesicles from total phospholipids of cold-adapted fish proved to be more disordered in all segments than from the warm-adapted ones whe n assayed using 2,12-(N-9-anthroyloxy)stearic and 16-(N-9-anthroyloxy) palmitic acid. Vesicles made from purified phosphatidylcholines showed the same pattern, but they were more disordered than the correspondin g total phospholipids. This could be modelled using mixed phospholipid vesicles made of synthetic 16:0/22:6 phosphatidylcholine (75%) and ei ther 18:1/22:6 phosphatidylethanolamine (25%) vs. 16:0/18:1 phosphatid ylethanolamine (25%) and comparison of the anisotropy parameters of 10 0% 16:0/22:6 and 100% 18:1/22:6 phosphatidylcholine vesicles. Mixing e ither 16:0/18:1 (25%) or 18:1/22:6 (25%) phosphatidylethanolamines to 18:0/22:6 (75%) phosphatidylcholine shifted down or up, respectively, the transition temperature of vesicles compared to 100% 18:0/22:6 vesi cles assayed by electron spin resonance spectroscopy using 5-doxylstea ric acid. It is concluded that it is not the gross amount of long-chai n polyunsaturated fatty acids in phospholipids, but rather their speci fic combination with cis Delta 9 monounsaturated fatty acids in the po sition sn-l, especially in phosphatidylethanolamines, that is importan t in determining the physical properties of biomembranes in relation t o adaptational temperature.