Chemistry and Biochemistry Faculty Works

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Browsing Chemistry and Biochemistry Faculty Works by Author "Capaldi, R. A."

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    Evidence for boundary lipid in membranes
    (Proceedings of the National Academy of Sciences, 1973-02) Jost, P. C.; Griffith, O. H.; Capaldi, R. A.; Vanderkooi, G.
    ABSTH\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.
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    Lipid‑protein and lipid‑lipid interactions in cytochrome oxidase model membranes
    (Journal of Supramolecular Structure, 1973) Jost, P. C.; Capaldi, R. A.; Vanderkooi, G.; Griffith, O. H.
    Two lipid environments are dete cted in membranous cyto chrome oxidase , using spin labeling techniques. This model membrane system consists of closed vesicular membranes formed spontaneou sly when the mem hr,jlne protein is isolated with its accompanying phospholipids. The data show both an immobili zed componen t, which is constant in amount , and a fluid componen t. Based on spectral analysis, the interpretation is that the bound component repre sents a single layer of lipid immobilized on the surface of the protein between the hydrophobic protein complex and the adjacent fluid bilayer regions. Maximal enzyme activity of this functional protein complex is attained when all of the bound sites are occupied , and above this level additional phospholipid (bilayer) has little or no effect on the enzyme activity .