Acetyl coenzyme A synthetase and the regulation of lipid synthesis from acetate in cultured cells.

The regulation of lipid synthesis from acetate in cultures of L cells in response to changes in exogenous lipid supply has been studied, and the enzyme acetyl-CoA synthetase has been investigated in reference to its possible role in the regulation of lipid biosynthesis from acetate. When serum lipid was removed from monolayers of L cells, a relatively rapid stimulation of [14C]acetate incorporation into lipid was observed within 2 hours. This stimulation of incorporation was observed in both sterol and fatty acid fractions. Conversely, an inhibition of [14C]acetate incorporation was observed within 1 to 2 hours when cells cultured in lipid-free medium were transferred to serumsupplemented medium. As with the stimulation, this inhibition was observed both in sterol and fatty acid fractions of the cell lipid. The data indicated a coordination of fatty acid and cholesterol metabolism in the cells. Inhibition of [14C]acetate incorporation was observed in sterol as well as free fatty acid and glycerolipid fractions in cultures grown in lipid-free medium and transferred to fatty acid-supplemented medium; and similarly, cultures transferred to medium supplemented with cholesterol showed inhibition not only of acetate incorporation into sterol but also into fatty acid and glycerolipid fractions. Cycloheximide, actinomycin D and mitomycin C seemed to have no influence on the early stimulation or inhibition of [r4C]acetate incorporation into total lipid. Acetyl-CoA synthetase activity was assayed in homogenates of L cells cultured in the presence of serum-supplemented or lipid-free medium and a 5-fold decrease in enzyme activity was observed in homogenates of cultures grown in the presence of exogenous lipid. When cells grown in serum-supplemented medium were transferred to serum-free medium, a stimulation of enzyme activity occurred within 2 to 3 hours which reached a maximum by 6 hours. Conversely, when cells were cultured in lipid-free medium and transferred to serum-supplemented medium, inhibition of enzyme activity occurred within the same time course.