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 DELTA6 desaturase in total and rough endoplasmic ret icula (ER and RER) was significantly higher in the CAS group than in t he SOY group. In ER and smooth endoplasmic reticulum, the steady-state fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, when incorp orated into the membrane, was decreased in the SOY group and accompani ed by a reduction in the cholesterol/phospholipid (CHOL/PL) ratio, con sistent with an increase in membrane fluidity. In a separate study, th e effect of varying dietary proteins, CAS, milk whey protein, egg albu min, SOY, potato protein and wheat gluten, on the relationship between the DELTA6 desaturase activity and microsomal membrane fluidity was a lso examined. The results indicated that the dietary protein-dependent change in the liver microsomal CHOL/PL ratio affected membrane fluidi ty, and subsequently the activity of DELTA6 desaturase in liver micros omes. However, since dietary protein influenced the DELTA6 desaturase activity in RER without influencing membrane fluidity, it is possible that some regulation might have taken place at the level of enzyme syn thesis.