MOLECULAR-SPECIES OF PHOSPHOGLYCERIDES IN LIVER-MICROSOMES OF RATS FED A FAT-FREE DIET

The influence of a fat-free diet on the molecular species composition of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosph atidylinositol (PI) of rat liver microsomes was studied by using rever sed-phase high-pressure liquid chromatography. In the three phosphogly ceride classes analyzed, the fat-free diet produced a large decrease i n the 18:0/20:4n-6 species but less important changes were found in th e 16:0/20:4n-6 species. In PC, the most abundant phosphoglyceride clas s of rat liver microsomes, the fall in the 18:0/20:4n-6 species was co unterbalanced mainly by an enhancement in the 16:0/18:1n-9 species alt hough it was not evident in PE. In PI, the decrease in the 18:4/20:4n- 6 species was counterbalanced by an increase in the 18:0/20:3n-9 speci es. Fluorescence polarization measurements of 1,6-diphenyl-1,3,5-hexat riene in liposomes of 16:0/18:1n-9-, 18:0/18:1n-9-, 16:0/20:4n-6-, and 18:0/20:4n-6-PC indicated that the change in the saturated fatty acid in the sn-1 position accompanying the replacement of 20:4n-6 by 18:1n -9 could be very important for a homeoviscous compensation, maintainin g the membrane physical properties without large alterations in spite of the essential fatty acid deficiency due to the fat-free diet.