The downfield aromatic (6-8 ppm) and upfield ring current shifted methyl regions (1-0 ppm) in the proton nuclear magnetic resonance spectrum of acyl carrier protein (ACP) from Escherichia coli have been examined at 500 MHz by using nuclear Overhauser methods. The data are analyzed in terms of the secondary structural model of Rock & Cronan (1979) [Rock, C. O., & Cronan, J. E., Jr. (1979) J. Biol. Chem. 254, 9778-9785], which suggests the existence of four alpha-helical segments joined by three beta-turns, and a short coil at the C terminus of the protein. Nuclear Overhauser effects among Tyr-71, Ile-69, Ile-72, and His-75 allow refinement of the secondary structure of the C terminus. Nuclear Overhauser effects among Tyr-71, Phe-28, and three Ile's also place stringent limitations on the folding of the four alpha-helices. These data allow the proposal of a tertiary structural model for ACP.

Residual quadrupole splittings for deuterons on perdeuterated a-and (3-D-mannose oriented in a potassium laurate liquid crystal have been measured. Multiple quantum two-dimensional NMR spectroscopy at high magnetic field is used to gain sufficient resolution to assign splittings to specific sites within these molecules. The assigned splittings are interpreted in terms of molecular geometries and preferred orientations of the molecules relative to the surface of the potassium laurate micelles that make up the liquid crystalline phase.The three-dimensional structures of complex carbohydrates and constituent sugars have become a topic of considerable interest over the last several years. It is now recognized that these molecules play central roles in cellular biology as structural components, as protective layers, as cell surface receptors, and as antigenic determinants (1, 2). Yet these molecules are among the least well characterized of biological macromolecules. Recent advances in high-resolution NMR, mass spectrometry, and diffraction studies (2-6) are providing new primary and secondary structural features, but progress toward an understanding of long-range folding in solution or the nature of membrane surface interactions is slow. Improved analytical methods capable of providing such information would be extremely valuable.Deuterium NMR has shown substantial promise as a probe of structural properties of both large and small molecules. This derives from the fact that this spin one nucleus displays both magnetic field-nuclear magnetic moment interactions and electric field gradient-nuclear quadrupole moment interactions. The former are defined in the laboratory frame by the application of a magnetic field. The latter are defined in the molecular frame by the distribution of electrons in chemical bonds, for example, a deuterium-carbon bond. In ordered systems, the manner in which the two interactions combine depends on the orientation of the bond relative to a molecular frame and on an order parameter matrix describing ordering of the molecule relative to the magnetic field. The interactions lead to two observable transitions for each site. At high field, for an axially symmetric bond in an axially ordered system, these transitions are split by 3e2qQ AVQ = 4h (1 -3 cos2)Sz. [1] e2qQ/h is a constant for a given bond type (170 kHz for deuterium bound to aliphatic carbons), 6 is the angle between the bond and averaging axis, and Sz is an order parameter (7). It is clear that information concerning orientation of molecular bonds or molecular order can be extracted from observation of deuterium spectra.Most applications of deuterium spectroscopy to date have used a known molecular geometry to extract order parameters. In a few liquid crystal studies, molecular geometries have been deduced (8)(9)(10)(11) Approximately 15 mg of mannose in 0.04 ml of H20 was added to 1.5 ml of this phase. The sample in a 10 mm NMR tube was placed in an 11.7-T superconducting magnet and allowed to equilibrate at 318 K for -1 hr...

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