Abstract
The saturation of the fat contained in the diet has been observed to affect the acylcoenzyme A:cholesterol acyltransferase (ACAT) activity of rat liver microsomes. ACAT activity in microsomes (Mp) prepared from livers of rats fed a polyunsaturated fat-enriched diet containing 14% sunflower seed oil was 70-90% higher than in microsomes (Ms) prepared from livers of rats fed a saturated fat-enriched diet containing 14% coconut oil. This difference was observed within 20 days after the diets were begun, the earliest time tested, and persisted throughout the 70-day experimental period. The difference was noted at all [1-14C]palmitoyl CoA concentrations tested, 2.5-33 micronM, and at temperatures between 18 and 40 degrees C. Arrhenius plots revealed a single transition in enzyme activity, occurring at 29 degrees C in both microsomal preparations. Likewise, the activation energy above this transition was the same in Mp and Ms, 12.5 KCal/mol. Addition of albumin to the incubation medium increased the ACAT activity of both microsome preparations, but the difference between Mp and Ms persisted. Mp was enriched in polyenoic fatty acids, primarily 18:2 and 20:4, while Ms was enriched in monoenoic acids. Although the 20:4 increase in Mp occurred in all phosphoglycerides, it was especially pronounced in the serine and inositol phosphoglyceride fraction. There were no differences in the phospholipid or cholesterol content, phospholipid head group composition, or protein composition of the two microsomal preparations. The possibility is discussed that the changes in ACAT activity result from the differences in fatty acid composition of the microsomes. Other microsomal enzymes exhibited varying responses to these dietary fatty acid modifications. Palmitoyl CoA hydrolase and NADPH cytochrome c reductase activities were unchanged. UDP glucuronyl transferase activity was 50% higher in Mp, but glucose-6-phosphatase and NADH cytochrome b5 reductase activities were 25% higher in Ms. Therefore, dietary fat modifications do not produce a uniform effect on the activity of microsomal enzymes.
Highlights
The saturation of the fat contained in the diet has been observed to affect the acylcoenzyme A:cholesterol acyltransferase (ACAT) activity of rat liver microsomes
When liver microsomes obtained from rats fed regular rodent chow were tested, incubation with these liposomes produced some increase in ACAT activity
The microsomes isolated from rats fed the diet enriched in saturated fat (M,) contained more monoenoic and less polyenoic fatty acids than those isolated from the rats fed the polyunsaturated fat-enriched diet (Mp).These differences are accounted for primarily by increases in the 16:ll and 18:l content of M, as opposed to increases in the 18:2 and 20:4 content of M
Summary
Weanling male Sprague-Dawley rats weighing 65 & 2 g were fed a semisynthetic diet consisting of 54% sucrose, 27% casein, 1% vitamin mix, and 4% mineral mix (Teklad Mills, Madison, WI) supplemented with either 14% sunflower oil (Cargill, Inc., Minneapolis, M N ) o r 14%coconut oil (Ruger Chemical Co., lrvington, NJ). T h e animals were housed in a room maintained at 20-22°C with lights on from 0700 to 1900 hr
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