| Abstract: | The mechanism of action of serum lipoproteins and 25-hydroxycholesterol on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity in hepatoma tissue culture (HTC) cells was investigated using antiserum against purified rat liver HMG-CoA reductase (Heller, R. A., and Shrewsbury, M. A. (1976)J. Biol. Chem. 251, 3815-3822). This antiserum cross-reacted with solubilized and membrane-bound HMG-CoA reductase from HTC cells. The enzymes from rat liver and HTC cells appeared antigenically identical. The increase in HMG-CoA reductase activity of HTC cells grown in medium which lacked serum lipoproteins was shown to be due to an increase in immunoprecipitable enzyme. In contrast, the 25-hydroxycholesterol suppression of reductase activity leads to a reduction in the antigenicity of the enzyme rather than a decrease in its number of molecules. |
