An efficient method for the production of isotopically enriched cholesterol for NMR

Abstract

13 C-Cholesterol was produced with high effi ciency by a genetically engineered yeast strain. The method produces ̃ 1 mg of cholesterol per gram of glucose using 100 ml of culture medium. Uniform 94% enrichment where the most abundant product is the fully enriched isotopomer ( u- 13 C 27 ) is obtained using ( u- 13 C 6 , 99%) glucose medium. High enrichment is very important for relaxation experiments, but for NMR applications where carbon-carbon couplings are measured, this is problematic. A good compromise between sensitivity and cost consists in diluting ( u- 13 C 6 , 25%) with natural-abundance glucose. With a 2:3 ratio, the maximal amount of singlets can be obtained in 1 dimensional (D) carbon and 2D heteronuclear single-quantum correlation (HSQC) spectra with 6× intensity increase relative to natural-abundance samples. The use of (1- 13 C 1 -glucose , 99%) or (2- 13 C 1 -glucose, 99%) as isotope sources allows the labeling of the cholesterol in multiple mostly nonvicinal positions and reach 45× intensity increase. As an alternative, the dilution of ( u- 13 C 6 , 99%) glucose can be used to simultaneously enrich eleven pairs of 13 C up to ̃ 1,000 × natural-abundance probability, which should be very beneficial to doublequantum NMR experiments including the INADEQUATE and related pulse sequences. The flexibility of the method and the potential to adapt the culture protocol to specific needs should fi nd many applications in chemistry and biology and in different fields of NMR and MS. Copyright © 2011 by the American Society for Biochemistry and Molecular Biology, Inc.