A new specific cholesterol assay gives reduced cholesterol/phospholipid molar ratios in cell membranes.

Extraction and analytical methods for estimating the cholesterol/phospholipid molar ratio in cell membranes were compared. It was important to extract the membrane or cells in saline suspension, as phospholipid was lost on drying the material. The phospholipid analytical methods were found to be satisfactory. The method of analyzing for cholesterol using the enzyme cholesterol oxidase produced results in agreement with those from gas chromatography. Older less specific analytical methods gave cholesterol results which were 10–33% higher. The human tonsil lymphocyte was found to have a cholesterol/phospholipid molar ratio of 0.30 ± 0.02, and the human erythrocyte plasma membrane had a ratio of 0.72 ± 0.03.