Conjugated polyene fatty acids as membrane probes: preliminary characterization.

The use of fluorescent conjugated polyenoic fatty acids as probes of membrane structure is introduced. alpha- and beta-parinaric acid (cis, trans, trans, cis-, and all trans-9,11,13,15-octadecatetraenoic acid) and synthetic lecithins containing an alpha-parinaric acid chain in position 2 are prepared and their absorption and fluorescence properties are determined. Phase transitions are detected as fluorescence changes at characteristic temperatures when either the free fatty acid probes or the labeled phospholipid probe are included in sonicated aqueous dispersions of L-alpha-dimyristoyl lecithin, L-alpha dipalmitoyl lecithin, or L-alpha-distearoyl lecithin. The phase transitions are detected at about 23 degrees C (dimyristoyl), 44 degrees C (dipalmitoyl), and 53 degrees C (distearoyl lecithin). Binding of alpha-parinaric acid to bovine serum albumin is measured by shifts in the absorption spectrum and enhanced quantum yield of the fatty acid upon binding and by energy transfer between 2 tryptophyl residues in bovine serum albumin and alpha-parinaric acid. Approximately six binding sites are detected. Other applications of these probe molecules, including phase transitions of phospholipid/cholesterol dispersions, induced circular dichroism of parinaric acid bound to albumin, and biosynthetic incorporation of parinaric acid into biological membranes, are discussed.