Studies were carried out to determine whether or not oxygenated derivatives of cholesterol (e.g., 25-hydroxycholesterol) that specifically suppress the activity of 3-hydroxy-3-methylglutaryl-CoA reductase [mevalonate:NADP + oxidoreductase (CoA-acylating), EC 1.1.1.34], bind to a soluble component of the cytoplasm different from that which binds the nonsuppressor, cholesterol. Density gradient fractionation of the cytosolic fraction isolated from L cell cultures that had been incubated with low concentrations of 25-hydroxy[ 26,27 - 3 H]cholesterol or [ 1,2 - 3 H]cholesterol provided evidence for the existence of at least two different sterol-binding proteins. Bound cholesterol sedimented in a sucrose density gradient as two or more broad bands with coefficients of approximately 9 S and 21 S. Two relatively narrow bands of bound 25-hydroxycholesterol had sedimentation coefficients of 5 S and 8 S. Preincubation of the cells with a relatively high concentration of unlabeled 25-hydroxycholesterol altered the banding pattern of the 25-hydroxy[ 3 H]cholesterol taken up during a subsequent incubation period by decreasing the size of the major (8S) band. Under these conditions, cholesterol did not affect the banding pattern of 25-hydroxy[ 3 H]cholesterol. The density gradient banding pattern of bound [ 3 H]cholesterol was only slightly affected by preincubating the cells with unlabeled cholesterol or 25-hydroxycholesterol. Both sterols appeared to be bound to proteins because the bound sterols were eliminated from cytosol that had been heated at 100°, and their sedimentation coefficients were altered by proteolysis.

Kandutsch, A. A., Chen, H. W., & Shown, E. P. (1977). Binding of 25-hydroxycholesterol and cholesterol to different cytoplasmic proteins. Proceedings of the National Academy of Sciences, 74(6), 2500–2503.