An X-ray study of the cytoplasmic membranes of two gram-positive bacteria.

X-ray diffraction diagrams of partially disordered one-dimensional lattices of isolated bacterial cytoplasmic membranes are described and they provide a basis for suggesting possible molecular structures of bacterial membranes. Biochemical and electron microscope evidence points towards a lipid bilayer with a high degree of fluidity. The protein molecules are in a disordered configuration in the membrane.

Deuterium nuclear magnetic resonance studies of potato starch hydration.

Deuterium Nuclear Magnetic Resonance (NMR) measurements at 4.7 Tesla were used to study the hydration properties of potato starch suspensions as a function of the starch-to-water ratio. The deuterium NMR spectrum of potato starch suspensions consisted of a relatively tall, single Lorentzian (D2O) peak and a resolved doublet ('powder' pattern) of about 1 kHz quadrupole splitting and low amplitude. The deuterium NMR transverse relaxation rate (R*2) was measured for the single Lorentzian, deuterium oxide peak; this rate increased with increasing starch-to-water ratio. Deviations of such R*2 dependences from linearity were observed only at high ratios of starch-to-water, above approximately 40% solids. In addition to the 'free' or bulk population (which has a very fast rotational correlation time of 5 ps), a second population of water weakly sorbed on the starch granule surface was monitored and found to be in fast exchange with the bulk water; this second water population has a rotational correlation time of 17 ps at 298 K, only about three times slower than that of bulk water. Additionally, a third population of slowly exchangeable water is present, which is "anisotropically bound" and has a highly restricted motion within the potato starch granule structure; well-defined quadrupole splittings are observed from this latter population of water in potato starch. Potato starch exhibits unique hydration properties that have not been found in cereal starches.

Molecular dynamics of water in foods and related model systems: multinuclear spin relaxation studies and comparison with theoretical calculations.

A review of recent studies of molecular dynamics of water in foods and model systems is presented, and the theoretical results are compared with experimental data obtained by several techniques. Both theoretical and experimental approaches are discussed for electrolytes, carbohydrates, and food proteins in solution. Theoretical results from Monte Carlo simulations are compared with experimental NMR relaxation data for quadrupolar nuclei such as those of deuterium and oxygen-17. Hydration studies of wheat, soybean, corn, and myofibrillar proteins by multinuclear spin relaxation techniques are discussed, and several new approaches to the analysis of the experimental data are considered. Correlation times of water motions in hydrated food systems are determined from NMR and dielectric relaxation data. The values of the correlation times for dilute solutions of electrolytes and carbohydrates estimated by NMR are in good agreement with those calculated from dielectric relaxation data, but seem to differ significantly from those proposed from Monte Carlo simulations. Several new and important results concerning the hydration of potato and cereal starches are presented, showing the very different hydration behaviors of these two major groups of starches. The combination of molecular dynamics computations with NMR relaxation techniques will hopefully stimulate novel technological developments in food engineering based on such fundamental studies.

Oxygen-17 and deuterium nuclear magnetic relaxation studies of lysozyme hydration in solution: field dispersion, concentration, pH/pD, and protein activity dependences.

A comparison of 17O and 2H NMR relaxation rates of water in lysozyme solutions as a function of concentration, pH/pD, and magnetic field suggests that only 17O monitors directly the hydration of lysozyme in solution. NMR measurements are for the first time extended to 11.75 T. Lysozyme hydration data are analyzed in terms of an anisotropic, dual-motion model with fast exchange of water between the "bound" and "free" states. The analysis yields 180 mol "bound" water/mol lysozyme and two correlation times of 7.4 ns ("slow") and 29 ps ("fast") for the bound water population at 27 degrees C and pH 5.1, in the absence of salt, assuming anisotropic motions of water with an order parameter value for bound water of 0.12. Under these conditions, the value of the slow correlation time of bound water (7.4 ns) is consistent with the value of 8 ns obtained by frequency-domain fluorescence techniques for the correlation time associated with the lysozyme tumbling motion in solutions without salt. In the presence of 0.1 M NaCl the hydration number increases to 290 mol/mol lysozyme at pD 4.5 and 21 degrees C. The associated correlation times at 21 degrees C in the presence of 0.1 M NaCl are 4.7 ns and 15.5 ps, respectively. The value of the slow correlation time of 4.7 ns is consistent with the calculated value (4.9 ns) for the lysozyme monomer tumbling in solution. The systematic deviations of the relaxation rates, estimated with the single-exponential approximation, from the theoretical, multiexponential nuclear (I' + 1/2) spin relaxation are evaluated at various frequencies for 17O (I = 5/2) with the first-order, linear approximation (25). All NMR relaxation data for hydrated lysozymes are affected by protein activity and are sensitive both to the ionization of protein side chains and to the state of protein aggregation.

Origin and behavior of deuteron spin echoes in selectively labeled amino acids, myoglobin microcrystals, and purple membranes.

We have obtained deuterium NMR spin-echo spectra of crystalline DL-[gamma-2H6]valine, [S-methyl-2H3]-methionine, cyanoferrimyoglobin from sperm whale (Physeter catodon), containing deuteriomethyl groups at methionine-55 and methionine-131, and [gamma-2H6]valine-labeled bacteriorhodopsin in the purple membrane of Halobacterium halobium R1. By using 90-tau-beta 90 degrees (XY) and 90-tau-beta 0 degrees (XX) pulse sequences and observing the dependence of the spin-echo amplitude upon the interpulse spacing tau, we have determined that the so-called "quadrupole echoes" obtained in these typical selectively deuterated condensed-phase biological systems are in fact strongly modulated by proton-deuteron and deuteron-deuteron dipolar interactions. The two amino acids and the protein crystals behaved as typical organic solids, with no evidence of "liquid-like" behavior, even in the presence of excess water (in the case of the ferrimyoglobin crystals). However, with the valine-labeled bacteriorhodopsin, the tau-dependence of XY echoes as a function of temperature emphasized the "solid-like" behavior of the membrane "matrix", while the basic nature of the spin-echo response for the narrow central component of the spectrum clearly indicated the very "fluid" or "mobile" nature of a series of residues that are shown elsewhere [Keniry, M., Gutowsky, H. S., & Oldfield, E. (1984) Nature (London) 307, 383-386] to arise from the membrane surface. Our results thus suggest that such NMR methods may yield useful information on side-chain dynamics complementary to that of line-shape and spin-lattice relaxation time analyses.

NMR study of chloride ion interactions with thylakoid membranes.

The role of Cl(-) in photosynthetic O(2) evolution has been investigated by observing the (35)Cl NMR linewidth under a variety of conditions in aqueous suspensions of chloroplasts, primarily for the halophytes Avicennia germinans, Avicennia marina, and Aster tripolium but also for spinach. The line broadening shows there is weak, ionic binding of Cl(-) to thylakoids, the bound Cl(-) exchanging rapidly (>>10(4) sec(-1)) with free Cl(-) in solution. The binding is necessary for O(2) evolution to occur. Michaelis-Menten constants obtained from the Cl(-) dependence of the O(2) evolution rate are approximately 15-70 mM for the halophytes compared with 0.6 mM for spinach (0.5 mM with Br(-)). There appear to be two types of Cl(-) binding sites in halophytes, of which the stronger is the activator, at lower [Cl(-)], of O(2) evolution. The (35)Cl line broadening includes a nonspecific interaction, which becomes apparent at high Cl(-) concentrations (>/=0.5 M).

Oxygen-17 and deuterium nuclear magnetic resonance studies of lysozyme hydration.

Oxygen-17 and deuterium NMR studies of lysozyme hydration are reported for a wide range of lysozyme concentrations, and the relationship between water "activity" and water mobility in the lysozyme-water system as determined by high-field NMR is examined. In a first approximation, the effect of lysozyme activity on hydration is considered to be small because of the relatively low charge on lysozyme at pH 7 and the absence of salt in the lysozyme solutions. Correlation times are determined for tightly bound water, weakly bound water, and "multilayer" or trapped water in lysozyme at 20 degrees C. Hydration numbers are also determined for these three different water populations interacting with lysozyme. Good agreement is found between the hydration numbers determined by 17O NMR and the calculations based on the D'Arcy and Watt analysis of water sorption isotherms for proteins that considered three major water populations in hydrated lysozyme. A molecular interpretation for the three components in the D'Arcy and Watt theory of sorption isotherms is also proposed on the basis of our NMR results. Previous proton NMR spin-echo results are shown to be consistent with our findings by 17O NMR and support the view that there are at least four regions of distinct hydration behavior of lysozyme which span the whole range from solutions to solid powders.

Multinuclear spin relaxation and high-resolution nuclear magnetic resonance studies of food proteins, agriculturally important materials and related systems.

An overview of the applications of Nuclear Magnetic Resonance (NMR) techniques in Agriculture and Food Chemistry, covering high-resolution, solid-state, pulsed gradient and two-dimensional techniques is presented. The systems investigated by such techniques range from purified proteins to mixtures, starch granules and wheat grains. Both hydration and structural/composition approaches that employ NMR techniques are discussed from the point of view of applications rather than technique development. Hydration models derived from multinuclear studies are discussed for food proteins and enzymes. The role of protein-protein interactions in the analysis of the NMR results on hydration is also discussed. Amongst the food proteins considered are: wheat gliadins, glutenins, corn zeins, soy glycinins and conglycinins, as well as muscle proteins. Several new applications and new directions of development of NMR in Agriculture and Food Chemistry are suggested, and potential practical applications are pointed out.