The specific activities of acetyl CoA carboxylase and fatty acid synthetase were measured in the cytosol fraction of livers from chicks fed various levels of corn oil, cottonseed oil, corn oil free fatty acids, or crude (79%) oleic acid. Activities of both enzymes were depressed by the addition of fat to a fat free basal diet. The ratios of synthetase to carboxylase activity were greater than unity when up to 4% fat was fed, but less than unity when 8% or higher levels of fat were fed. The depressions of the activities of these enzymes appeared to be unrelated to the dietary level of linoleate. In in vitro experiments, 2 μM concentrations of palmityl CoA or oleoyl CoA depressed acetyl CoA carboxylase activity. Concentrations of 20 μM of these acyl CoA esters did not affect the activity of fatty acid synthetase.
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