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The NMR features of bradykinin were investigated in dimethylsulfoxide containing 1% water. The temperature dependence of chemical shifts and ROESY maps were monitored for the major species where all X±Pro bonds are trans. The occurrence of a head-to-tail ionic interaction and intramolecular hydrogen bonds stabilizing a pseudo cyclic arrangement was inferred, a b turn at the C-terminus being the main feature of the secondary structure. Calcium was shown to bind to the peptide with a dissociation constant K d = 2.8 + 0.2 mm.2 Pro and 3 Pro carbonyls, as well as the 9 Arg carboxyl, were assigned as the metal-binding sites. A molecular model of the 1 : 1 metal± complex was obtained. In light of conformational changes experienced by the peptide upon interaction with calcium, a role for the metal was hypothesized in the process of conformational selection from the free to the receptor-bound state of bradykinin.Keywords: bradykinin; calcium; conformational selection; NMR.The activity of the two main kinin peptides (bradykinin, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Ser, and kallidin, Lys-bradykinin), is mediated by a G-protein-coupled receptor (B2) expressed in nearly all cells. Receptor activation causes a cascade of events [1]; kinins have therefore been implicated as relevant mediators in several pathophysiologies, including the peripheral inflammatory processes associated with Alzheimer's disease [2].Links between calcium homeostasis and/or signalling and the stimulation of kinin receptors in mammalian cells have been well established by an enormous body of literature, especially in recent years (e.g. Refs 3±5). However, to our knowledge, the direct effect of calcium upon the conformational equilibria of kinin peptides in solution has not been investigated so far, in spite of the attainable beneficial information.The presence of three prolines in the sequence is expected to yield structural heterogeneity in solution, because the cis-trans interconversion at each X±Pro bond may provide up to eight stable isomers, depending on environmental parameters. Several CD and NMR investigations in a number of solvent systems have occasionally detected transient ordered structures, similar to g turns and b turns [6±23]; however, the net result of a random coil peptide was obtained in all cases due to the fast rate of exchange between the extended structures. Such a high degree of flexibility suggests that binding to the receptor implies the selection of a particular structure from among the number of slowly or rapidly interconverting ones in solution. As a matter of fact, enhancement of the b-turn-forming potential of bradykinin was observed in the presence of SDS micelles [16,24±27], apolar organic solvents [14,18,20,27] or aqueous phospholipids [13,22,26]; as a consequence of all these findings, bradykinin is currently believed to adopt a C-terminal b turn upon complexation with the receptor [28].In the present study, NMR data were collected for bradykinin in dimethylsulfoxide containing 1% water in the presence of calcium, in orde...

Many processes have been proposed to produce glucose as a substrate for bacterial fermentation to obtain bioethanol. Among others, cellulose degradation appears as the most convenient way to achieve reliable amounts of glucose units. In fact, cellulose is the most widespread biopolymer, and it is considered also as a renewable resource. Due to extended intra- and interchain hydrogen bonds that provide a very efficient packing structure, however, cellulose is also a very stable polymer, the degradation of which is not easily achievable. In the past decade, researchers enhanced cellulose reactivity by increasing its solubility in many solvents, among which concentrated phosphoric acid (H(3)PO(4)) played the major role because of its low volatility and nontoxicity. In the present study, the solubilization mechanism of crystalline cellulose in H(3)PO(4) has been elucidated by using high- and low-field NMR spectroscopy. In particular, high-field NMR spectra showed formation of direct bonding between phosphoric acid and dissolved cellulose. On the other hand, molecular dynamics studies by low-field NMR with a fast field cycling (FFC) setup revealed two different H(3)PO(4) relaxing components. The first component, described by the fastest longitudinal relaxation rate (R(1)), was assigned to the H(3)PO(4) molecules bound to the biopolymer. Conversely, the second component, characterized by the slowest R(1), was attributed to the bulk solvent. The understanding of cellulose dissolution in H(3)PO(4) represents a very important issue because comprehension of chemical mechanisms is fundamental for process ameliorations to produce bioenergy from biomasses.

Different "average" nuclear magnetic resonance relaxation times for correlation with fluid-flow permeability and irreducible water saturation in water-saturated sandstones In 1 H NMR ͑nuclear magnetic resonance͒ relaxation measurements for a set of eight hardwood and softwood samples, each free induction decay ͑FID͒ is fitted by the sum of a "solid" signal of the form A exp͓−c͑t / T S ͒ 2 ͔͓1−g͑t / T S ͒ 2 + h͑t / T S ͒ 4 ͔ plus a "liquid" signal B exp͑−t / T 2-FID ͒. Distributions of longitudinal ͑T 1 ͒ relaxation times were computed separately for the solid and liquid components, giving also the solid/liquid 1 H ratio ␣. From measurements on the samples dried, seasoned, and hydrated, the moisture content ͑liquid/solid weight ratio͒ was found to be approximately 0.50/ ␣. For each of the "seasoned" samples ͑10%-13% moisture content͒ a single T 1 peak was found for the solid and two for the liquid, with the longer liquid T 1 close to that of the solid, but with some differences exceeding perceived experimental uncertainties. None of the solid or liquid-long T 1 's is much less than 20 ms, even though liquid-short times go as low as 0.35 ms, appearing to negate simple solid-to-liquid exchange on a millisecond time scale. Data for six of the samples ͑all except for two resin-containing pine species͒ can be formally fitted by a two-site exchange model, in which cases the solid-to-liquid exchange times are a few tens of milliseconds. For our set of wood samples, each of the above three T 1 values, and also the overall liquid geometric-mean and rate-average T 1 's, as well as the liquid long-T 1 fraction, for a seasoned hardwood is longer than the corresponding value for any softwood, suggesting that relaxation parameters may provide a useful ranking of seasoned woods.

A number of pistachio oils were selected in order to test the efficacy of nuclear magnetic resonance relaxation dispersion (NMRD) technique in the evaluation of differences among oils (1) obtained from seeds subjected to different thermal desiccation processes, (2) retrieved from seeds belonging to the same cultivar grown in different geographical areas and (3) produced by using seed cultivars sampled in the same geographical region. NMRD measures relaxation rate values which are related to the dynamics of the chemical components of complex food systems. Results not only allowed to relate kinematic viscosity to relaxometry parameters but also were successful in the differentiation among the aforementioned oils. In fact, from the one hand, the larger the kinematic viscosity, the faster the rotational motions appeared as compared to the translational ones. On the other hand, relaxation rate curves (NMRD) varied according to the oxidative stresses and chemical composition of each sample. The present study showed for the first time that NMRD is a very promising technique for quick evaluations of pistachio oil quality without the need for time-consuming chemical manipulations.