Effect of different amino acid diets on delta 5, delta 6 and delta 9 desaturases.

A high-protein diet with 45% calories from casein increased delta 6 desaturase activity in rat-liver microsomes. High-protein diets with 45% calories from a synthetic mixture of amino acids in the same proportion as casein decreased the delta 9 desaturase, slightly increased the delta 5 desaturase and greatly increased delta 6 desaturase activities compared with a high-carbohydrate diet. The elimination of phenylalanine and tyrosine from the synthetic mixtures of amino acids increased the delta 6 desaturase activity. Massive amounts of phenylalanine or tyrosine in the diet inhibited delta 6 desaturase activity. Tyrosine and phenylalanine may, by conversion to tyrosine, decrease the activity of the delta 6 desaturase.