Studies of differential turnover of palmitoyl and stearoyl species of glycerophosphatides using labeled unsaturated acids

Normal and bile fistula rats were injected with 1‐ 14 C‐linoleate and arachidonate as albumin complex and the glycerides and glycerophosphatides of the liver and bile were isolated at various time intervals. The distribution of radioactivity among the individual molecular species was determined by thin layer and radio gas chromatography and specific enzymic hydrolyses. At 30 min after administration of linoleate 30% of the radioactivity in liver was in lecithins and 8% in cephalins, while at 120 min 48% was in lecithins and 16% in cephalins. After arachidonate, 58% and 64% of the counts were in lecithins and 12% to 13% in the cephalins at the above periods of sampling. The specific activity of the palmitoyl linoleoyl lecithins and cephalins was two to three times higher than that of the corresponding stearoyl linoleoyl species, which was of the same order but much lower magnitude than found previously for lecithins using labeled phosphate and choline. The palmitoyl and stearoyl species of arachidonoyl lecithins possessed equal specific activities, in sharp contrast to previous findings with radioactive phosphate, which showed a 12 times higher specific activity for the palmitoyl arachidonate. The palmitoyl arachidonoyl cephalins had two to three times greater specific activity than the corresponding stearoyl species in agreement with previous work using labeled phosphate. The distribution of radioactivity suggests that the arachidonate was incorporated into the lecithins largely via acyl transfer, while the linoleate contributed to both acyl transfer and de novo synthesis. Interpretation of the mechanism of uptake of these acids into the cephalins awaits further studies.