Jost, P. C.Griffith, O. H.Capaldi, R. A.Vanderkooi, G.2016-05-252016-05-251973-02Jost, P. C., Griffith, O. H., Capaldi, R. A. & Vanderkooi, G. (1973) Evidence for boundary lipid in membranes. Proc. Natl. Acad. Sci. USA 70, 480‑484.https://hdl.handle.net/1794/198886 pagesABSTH\OT (Mochromc oxidase (EC 1.9.3.1) isolated from hccf-hcarl mitochondria with an appropriate phospholipid content forms vesicular structures. Lipid-protein interactions in this model membrane system were studied with the,lipid spin label, 16-doxylstearic acid. As the phospholipid/ prolein ratio is varied, two spectral components are ohserved. Al low phospholipid/prolcin ratios (<0.19 mg of phospholipid per mg of protein) the lipid spin label is liifCll!) immobilized. At higher phospholipid content an additional component characteristic of fluid lipid hilayers is evideiil. By summation of digilalized spectra and subsequent integration it was shown that all composite spec tra could he approximated by assuming only two com ponents arc present, and that the amount of phospholipid hound In Ihr protein is independent of the extent of the fluid hilaw-r region. The experimentally determined amount of phospholipid for maximum occupancy of pro- Iciii-hound niies is ahouI 0.2 mg of phospholipid per 1.0 nig itl protein. Iialiulalions show that this ralio is con sistent with a single layerof phospholipid surrounding the protein complex. The data are interpreted as evidence for a boundary of immobilized lipid between the hydrophobic protein and adjacent fluid hilayer regions in this membrane model system.en-USCreative Commons BY-NC-ND 4.0-USArticle