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Utilization of Methionine for Phospholipid Formation as Affected by Dietary Protein in the Rat¹

Department of Biochemistry and School of Human Development, Maine Agricultural Experiment Station, University of Maine, Orono, Maine 04473

Phospholipids were isolated from the livers and brains of rats which had been force-fed L-methionine-methyl-¹⁴C 3 hours previously. The rats had been fed three diets—amino acids (AA), casein-lactalbumin (CL) and wheat gluten (WG)—which had been made up to the FAO pattern in essential amino acids and to the same total nitrogen (N) concentration. These diets were fed to rats at two levels, 1.2 and 1.6% of N, for 2 weeks. The ¹⁴C-activity of liver phospholipids reached a peak after 3 hours and began to decrease. The ¹⁴C-activity of the brain phospholipids continued to rise for at least 8 hours, but the greatest rate of increase occurred between 3 and 5 hours after the force-feeding of the radioactive methionine. There was no difference in the liver or brain in the degree of conversion of the methyl-¹⁴C activity from methionine to phospholipids due to the AA, CL or WG diets. In the liver, the groups fed 1.2% of dietary N showed a significantly higher conversion of the methyl-¹⁴C from methionine to phospholipids than the groups fed 1.6% of dietary N. In the brain the groups fed 1.6% of dietary N showed a greater relative conversion of the methyl-¹⁴C to phospholipids than the group receiving 1.2% of dietary N.

KEY WORDS: • methionine • phospholipid • protein

¹ This study was part of Northeastern Regional Project NE-52, Utilization of amino acids from protein, and was supported in part by Regional Research Funds.

Manuscript received 12 July 1972.