Enzyme inhibition during the conversion of squalene to cholesterol

Donald Lewis, Helen Galczenski, Saul Needle, Sheng Yuh Tang, Dilip Amin, Marie Gleason, Glenda Bilder, Mark Perrone, Linda Merkel, Camilo Rojas

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Two separate enzymatic assays were developed in order to test the selectivity of inhibitors in cholesterol biosynthesis. One assay detects inhibition of Δ5,7-sterolΔ7-reductase, the enzyme involved in the conversion of 7-dehydrocholesterol to cholesterol. Δ5,7-SterolΔ7-reductase was inhibited by both RPR 101821, a protonated cyclohexylamine, and BM 15.766, a piperazine derivative, with IC50 values of 1 μM. The second assay detects accumulation of any of five intermediates (squalene oxide, squalene dioxide, lanosterol, desmosterol, and 7-dehydrocholesterol) upon inhibition of enzymes catalyzing reactions in the conversion of squalene to cholesterol. In this assay, inhibition data were most accurate when control assays exhibited a conversion of squalene to cholesterol in the order of 50%. The time required to attain 50% conversion of squalene to cholesterol was 6 h. Given a high inhibitor to substrate concentration ratio and the possible values of Ki, kon, and koff for the reaction between enzymes and inhibitor to form enzyme-inhibitor complexes, it was predicted that in the presence of inhibitors, intermediate accumulation could still be observed after 6 h incubation. The experimental results were in agreement with this prediction.

Original languageEnglish (US)
Pages (from-to)475-483
Number of pages9
Issue number7
StatePublished - Jul 1995
Externally publishedYes


  • cholesterol
  • dehydrocholesterol
  • inhibition
  • reductase
  • squalene
  • sterol

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Endocrinology
  • Pharmacology
  • Clinical Biochemistry
  • Organic Chemistry


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