Protein-Lipid Interactions. High-Field Deuterium and Phosphorus Nuclear Magnetic Resonance Spectroscopic Investigation of the Cytochrome Oxidase-Phospholipid Interaction and the Effects of Cholate†

Deuterium quadrupole-echo Fourier transform nuclear magnetic resonance spectra (at 34 MHz) and phosphorus-31 Fourier transform nuclear magnetic resonance spectra (at 60.7 MHz) have been obtained of l-(6,6-dideuteriopalmitoyl)-2-oleyl-sn-glycero-3-phosphocholine dispersions in excess water in the absence of, and complexed with, the membrane enzyme cytochrome oxidase (cytochrome c:O2 oxidoreductase, EC 1.9.3.1). Thereby, we have investigated the effects of the detergent sodium cholate, and of temperature, on protein-lipid interactions in this system. Our results strongly suggest that residual detergent in these protein-lipid complexes causes a significant disordering of hydrocarbon chain and head group organization as determined by deuterium quadrupole splittings (Δ VQ) and phosphorus chemical shielding anisotropics (Δ Δ). At low (~2 wt %) cholate levels, C6 ΔVQ and 31P Δσ values in the protein-lipid complexes (containing~70 wt % protein) are only about 8% smaller than in pure phospholipid bilayers at the same temperature, between 20 and 35 °C, suggesting rather similar structural organization. There are, however, significant line-width increases, especially on approaching Tc in both deuterium and phosphorus spectra, indicating increased correlation times, in the region of the membrane surface. These results obtained on protein-lipid complexes containing an unsaturated phospholipid are in agreement with those of a previous study utilizing a disaturated phospholipid [Kang, S. Y., Gutowsky, H. S., Hsung, J. C., Jacobs, R., King, T. E., Rice, D., & Oldfield, E. (1979) Biochemistry 18, 3257-3267] but differ significantly from those of a similar study employing l-(5,5-dideuteriopalmitoyl)-2-oleyl-sn-glycero-3-phosphocholine [Seelig, A., & Seelig, J. (1978) Hoppe-Seyler's Z. Physiol. Chem. 359, 1747-1756].