Effects of dietary proteins on linoleic acid desaturation and membrane fluidity in rat liver microsomes.

The effect of dietary protein, casein (CAS) and soybean protein (SOY), on linoleic acid desaturation in liver microsomes was studied in rats. The activity of delta 6 desaturase in total and rough endoplasmic reticula (ER and RER) was significantly higher in the CAS group than in the SOY group. In ER and smooth endoplasmic reticulum, the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, when incorporated into the membrane, was decreased in the SOY group and accompanied by a reduction in the cholesterol/phospholipid (CHOL/PL) ratio, consistent with an increase in membrane fluidity. In a separate study, the effect of varying dietary proteins, CAS, milk whey protein, egg albumin, SOY, potato protein and wheat gluten, on the relationship between the delta 6 desaturase activity and microsomal membrane fluidity was also examined. The results indicated that the dietary protein-dependent change in the liver microsomal CHOL/PL ratio affected membrane fluidity, and subsequently the activity of delta 6 desaturase in liver microsomes. However, since dietary protein influenced the delta 6 desaturase activity in RER without influencing membrane fluidity, it is possible that some regulation might have taken place at the level of enzyme synthesis.