Bicelle-based liquid crystals for NMR-measurement of dipolar couplings at acidic and basic pH values

It is demonstrated that mixtures of ditetradecyl-phosphatidylcholine or did odecyl-phoshatidylcholine and dihexyl-phosphatidylcholine in water form lyo tropic liquid crystalline phases under similar conditions as previously rep orted for bicelles consisting of dimyristoyl-phosphatidylcholine (DMPC) and dihexanoyl-phosphatidylcholine (DHPC). The carboxy-ester bonds present in DMPC and DHPC are replaced by ether linkages in their alkyl analogs, which prevents acid- or base-catalyzed hydrolysis of these compounds. N-15-H-1 di polar couplings measured for ubiquitin over the 2.3-10.4 pH range indicate that this protein retains a backbone conformation which is very similar to its structure at pH 6.5 over this entire range.