Characteristics of phospholipids in microvillar membranes of octopus photoreceptor cells.

Characteristics of lipids in the microvillar membranes of octopus photoreceptor cells were studied in order to obtain some information on the membrane environment with rhodopsin in the invertebrate. (1) The membranes contain lipid and protein in almost equal proportion. The majority of lipids are phospholipids. Neutral lipids make up 16% of the total lipids, the major constituent of which is cholesterol. (2) Phosphatidylethanolamine and phosphatidylcholine are the major phospholipids. Phosphatidylserine, ceramide 2-aminoethylphosphonate and sphingomyelin occur as minor components. An unidentified alkaline and acid stable phospholipid was found. (3) The predominant fatty acids of phosphatidylethanolamine and phosphatidylcholine are highly unsaturated such as 22 : 6, 20 : 5 and 20 : 4. The 22 : 6 and 20 : 5 are exclusively linked at the 2-position, but the 20 : 4 is linked significantly at the 1-position of the phospholipids. (4) Major molecular species are 16 : 0/22 : 6 (48.4%) and 16 : 0/20 : 4 (19.6%) in phosphatidylcholine, and 20 : 4/22 : 6 (50.7%) and 16 : 0/22 : 6 (25.6%) in phosphatidylethanolamine.