The cholesterol-to-protein ratio in DRM and non-DRM fractions is sensitive to a 6-fold difference in starting protein levels. DRMs were cholesterol rich and protein poor when prepared from a low starting protein concentration. Membranes were extracted using 1% Tx-100 from material containing either a high (7.5 mg/mL protein) or low (1.25 mg/mL protein) starting protein concentration and subjected to sucrose gradient centrifugation as described. For each fraction, the level of protein (A) and the cholesterol-to-protein ratio (B) were measured and calculated as described for Figures 1 and 2.