10.1021/acs.biochem.6b00286.s001 Ayumi Yamada Ayumi Yamada Nobutaka Shimizu Nobutaka Shimizu Takaaki Hikima Takaaki Hikima Masaki Takata Masaki Takata Toshihide Kobayashi Toshihide Kobayashi Hiroshi Takahashi Hiroshi Takahashi Effect of Cholesterol on the Interaction of Cytochrome P450 Substrate Drug Chlorzoxazone with the Phosphatidylcholine Bilayer American Chemical Society 2016 POPC ER membranes mol lipid bilayers DSC CYP drug metabolism process UV CYP substrate drugs cholesterol concentration dependence CZX Cytochrome P 450 Substrate Drug Chlorzoxazone membrane protein cytochrome P 450 PC bilayers CYP substrate drug 2016-06-27 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Effect_of_Cholesterol_on_the_Interaction_of_Cytochrome_P450_Substrate_Drug_Chlorzoxazone_with_the_Phosphatidylcholine_Bilayer/3473462 Many drugs are oxidized by membrane protein cytochrome P450 (CYP) enzymes during their metabolism process. CYPs are located mainly in endoplasmic reticulum (ER) membranes. Recent studies have suggested that CYP substrate drugs first bind the lipid bilayers of ER membranes and then the drugs reach the active site of CYP by way of an access channel. The entrance of the channel is located in the hydrophobic regions of the lipid bilayers. One of the features of the ER membrane is a cholesterol content that is lower than those of other biomembranes. In this study, the cholesterol concentration dependence of the interaction of a CYP substrate drug, chlorzoxazone (CZX), with model membranes composed of phosphatidylcholine (PC) and cholesterol was examined via differential scanning calorimetry (DSC), UV–visible spectroscopy, and X-ray diffraction. Experimental results indicated that CZX can bind to pure PC bilayers in the absence of cholesterol and that, by contrast, a high cholesterol concentration (30–50 mol %) tends to prevent CZX from binding to PC bilayers. Interestingly, the effect of cholesterol on the binding and insertion of CZX was biphasic. In the case of palmitoyloleoylphosphatidylcholine (POPC) bilayers containing 5–10 mol % cholesterol, the CZX’s binding and penetration into the bilayer were found to be greater than those with pure POPC bilayers. The concentration of 5–10 mol % nearly corresponds to the cholesterol concentration of ER membranes. The low cholesterol contents (12–20 mol %) of ER membranes might be the most suitable for the CYP drug metabolism process in ER membranes.