Effects of Amino Acid Composition of Dietary Protein on Linoleic Acid Desaturation in Rats

Abstract

Dietary protein-dependent differences in the linoleic acid desaturation in rats were studied in terms of the differences in the amino acid composition. Soybean protein and its amino acid mixture decreased the linoleate desaturation index, the ratio of (20:3 n-6 + 20:4 n-6)/18:2 n-6, in the liver microsomal phospholipids compared to the casein counterparts, accompanying an increase in the ratio of cholesterol/phospholipid. The Δ6-desaturase activity of the liver microsomes was lower in the soybean protein group than in the casein group. The arginine supplementation to the casein diet tended to decrease but the lysine supplementation to the soybean protein diet tended to increase the activity, although the response pattern of the desaturation index was not necessarily paralleled in the latter situation. The effect of cystine supplementation to the casein diet was also inconclusive. Therefore, the arginine level of dietary protein, rather than the lysine/arginine ratio and the cystine content, seemed to be more important in the regulation of linoleic acid desaturation.