Incorporation of Labelled Phosphate Into Phospholipids in Squid Giant Axons

Inorganic phosphate labelled with 32 P was applied to giant axons excised from squid ( Loligo pealeii ) by addition of 32 Pi to the bathing solution, by injection into the axon, or by addition to axoplasm which had been separated from the sheath. The preparations were kept at 10 to 25° for various times up to 4 hr. When 32 P i was supplied by way of the bathing solution, axoplasm and sheath were usually separated at the end of incubation before extraction of the lipids. Lipids were extracted with chloroform‐methanol and resolved by paper chromatography. The lipids which became labelled appeared to be the same in sheath and axoplasm. They were identified by cochromatography with known lipids and by chromatography of products formed from them by mild alkaline hydrolysis. They included phosphatidylinositol, phosphatidylethanolamine, phosphatidic acid, and probably somelysophosphatidylethanolamine. Some labelled components remained unidentified. Phosphatidylcholine was apparently present, but did not become significantly labelled either in sheath or in axoplasm, or in a squid's stellate ganglion. There was no evidence that separation from the sheath impaired the capacity of the axoplasm for lipid synthesis.