Fine structure of the proteinaceous substance in sieve tubes

Summary The dense pore-filling substance in the sieve plates of dicotyledons seems to consist of fibrils, rather than systems of membranes.

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Zusammenfassung Die dichte Substanz, welche bei Dicotyledonen die Poren der Siebplatten ausfüllt, scheint eher aus Fibrillen als aus Membransystemen zu bestehen.

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With 6 Figures in the Fext     

Fluorescence and Absorption Spectra of Biological Dyes

Data include charts and tables of absorbance and fluorescence of 4 coupling agents for immunity reactions, 34 typical fluorescent dyes and reagents, and 12 dyes or reagents having no fluorescence in solution but which may be fluorescent in the dry state. Since this report consists largely of reference data, the original must be consulted for details. Reprint source: The Perkin-Elmer Corporation, Norwalk, Connecticut, U. S. A.     

A specific cholesterol binding site is established by the 2.8 A structure of the human beta2-adrenergic receptor

The role of cholesterol in eukaryotic membrane protein function has been attributed primarily to an influence on membrane fluidity and curvature. We present the 2.8 A resolution crystal structure of a thermally stabilized human beta(2)-adrenergic receptor bound to cholesterol and the partial inverse agonist timolol. The receptors pack as monomers in an antiparallel association with two distinct cholesterol molecules bound per receptor, but not in the packing interface, thereby indicating a structurally relevant cholesterol-binding site between helices I, II, III, and IV. Thermal stability analysis using isothermal denaturation confirms that a cholesterol analog significantly enhances the stability of the receptor. A consensus motif is defined that predicts cholesterol binding for 44% of human class A receptors, suggesting that specific sterol binding is important to the structure and stability of other G protein-coupled receptors, and that this site may provide a target for therapeutic discovery.