Deuterium NMR and EPR of hydrated collagen fibers in the presence of salts

A new model for hydrated collagen fibers is postulated. According to this model, a part of the water adsorbed is bound to the collagen fiber through hydrogen bonding, and the rest is randomly reorienting. The two types of water are in chemical exchange. The observed dipolar splitting for H₂O and quadrupolar splitting for D₂O are time-averaged values. The deuterium quadrupole splitting of D₂O in oriented collagen fibers decreases in the presence of salt. The phenomenon can be explained either by a change in the structure of collagen or by the blocking of the water binding sites by the ions. In the EPR spectra of collagen presoaked in Mn(II) and Cu(II) sulfates, the line widths decrease with the increase of water content, indicating the coordination of the cations to water. The change in the hyperfine splitting (from 70 gauss in dry fibers to 96 gauss in fibers equilibrated at 100% RH) of Mn(II) with water content is explained by the change in the symmetry of its environment.     

Thermal perturbation difference spectra and D2O vs H2O isothermal difference spectra of protein-model aromatic chromophores.

The thermal perturbation difference spectra of phenolic and indolic chromophores in water resemble the isothermal D₂O and H₂O spectra of these chromophores. For phenols approximately equal Δ? values are obtained in both types of spectra, but for their methyl ethers Δ? values of D₂O vs H₂O spectra are about half of those of the thermal perturbation spectra. Phenols and their methyl ethers were studied in deuterated ethylene glycol and glycerol vs the corresponding protiated solvent, and in nonprotic solvents containing 0.25–4% D₂O or H₂O. For phenols in D₂O vs H₂O, about one-third to one-half of the difference spectrum is attributed to solvent structure difference, and the remainder to the effects of replacing OH by OD and to differences in accepting hydrogen bonds from D₂O and H₂O. The refractive index difference between D₂O and H₂O was shown to be a minor contribution by means of experiments in which D₂O was at 5 dgC and H₂O at 47 dgC, conditions of equal refractive index (Na_D). D₂O vs H₂O and glycerol-d vs glycerol-h difference spectra of ribonuclease are about twice as large as expected from the known number of exposed tyrosyl side chains. Possible sources of error in D₂O vs H₂O spectra of proteins are discussed.     

Sites of action of D2O in intact and skinned crayfish muscle fibers

Summary The effect on tension development of replacing 90% of the H₂O of the bathing saline with D₂O was studied on intact single fibers, and on skinned fibers before and after the latter were treated so as to eliminate Ca-accumulation by the sarcoplasmic reticulum (SR). Excitation-contraction coupling (ECC) of intact fibers is not abolished, but is depressed by D₂O so that higher depolarizations are required to elicit a given tension. The reduction in tension at a given level of depolarization is not due to inhibition of the contractile system. The latter showed an enhanced Ca sensitivity; that is, skinned fibers respond to Ca concentrations that are 1–2 orders of magnitude smaller in D₂O than in H₂O saline. When bathed in D₂O saline, intact fibers or skinned fibers with functional SR can still accumulate and release Ca in sufficient quantities to allow repeated induction of maximum tensions. Relaxation is slowed in all three types of preparation, perhaps because of an increased affinity of troponin to Ca in D₂O salines.     

Structural aspects of pressure effects on infrared spectra of mixed-chain phosphatidylcholine assemblies in D2O

The barotropic behavior of D2O dispersions of 1-stearoyl-2-caproyl-sn-glycero-3-phosphocholine, C(18):C(10)PC, a highly asymmetric phospholipid in which the length of the fully extended acyl chain at the sn-1 position of the glycerol backbone is twice as long as that at the sn-2 position, has been investigated by high-pressure Fourier transform infrared spectroscopy. This asymmetric phosphatidylcholine bilayer at room temperature displays a pressure-induced phase transition corresponding to the liquid-crystalline----gel phase transition at 1.4 kbar. A conformational ordering of the lipid acyl chains is observed to take place abruptly at the transition pressure of 1.4 kbar. However, the lamellar lipid molecules and their acyl chains remain to be orientationally disordered in the gel phase until the applied pressure reaches 5.5 kbar. In the gel phase of fully hydrated C(18):C(10)PC, the asymmetric lipid molecules assemble into mixed interdigitated bilayers with perpendicular orientation of the zigzag planes among neighboring acyl chains. The role of excess water played in the interchain structure and the behavior of excess water and bound water under high pressure are also discussed.     

New perspectives on collagen fibers in the squid mantle

The squid mantle is a complex structure which, in conjunction with a highly sensitive sensory system, provides squid with a wide variety of highly controlled movements. This article presents a model describing systems of collagen fibers that give the mantle its shape and mechanical properties. The validity of the model is verified by comparing predicted optimal fiber angles to actual fiber angles seen in squid mantle. The model predicts optimal configurations for multiple fiber systems. It is found that the tunic fibers (outer collagen layers) provide optimal jetting characteristics when oriented at 31°, which matches empirical data from previous studies. The model also predicted that a set of intramuscular fibers (IM‐1) are oriented relative to the longitudinal axis to provide optimal energy storage capacity within the limiting physical bounds of the collagen fibers themselves. In addition, reasons for deviations from the predicted values are analyzed. This study illustrates how the squid's reinforcing collagen fibers are aligned to provide several locomotory advantages and demonstrates how this complex biological process can be accurately modeled with several simplifying assumptions. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

The effect of vitamin D on the structural crosslinks and maturation of chick bone collagen.

The quantitative relationships were determined between the structural crosslinks, dihydroxylysinonorleucine (Lys(OH)2-Nle) and hydroxylysinonorleucine (Lys (OH) -Nle) in NaB 3H4-reduced diaphyseal bone collagen from 1-, 2-, 3- and 4-week-old chicks fed either a vitamin D-deficient diet, a normal-vitamin D diet or a high-, but non toxic, vitamin D diet from time of hatching. Chicks fed the normal diet showed a progressive decrease in the ratio of Lys(OH)2-Nle/Lys(OH)-Nle with age. This decrease was accelerated in chicks receiving the High-vitamin D diet. In the vitamin D-deficient group, the ratio was higher than controls at 1 and 2 weeks and increased further at 3 and 4 weeks. Similar changes in Lys(OH)2-Nle/Lys(OH)-Nle ratio did not occur in skin collagen. Compared to Control-vitamin D animals, the increased crosslink ratios in the vitamin D-deficient bone collagen occurred prior to changes in growth rate and could not be correlated with lysine hydroxylation or the hypocalcemia seen in this group. These results suggest that the type of crosslink analysis used in this study provides one of the earliest and most sensitive indications of a bone disturbance due to vitamin D deficiency and that vitamin D specifically acts to increase the rate of maturation of bone collagen.     

Motional narrowing of the 2H NMR spectra near the chain melting transition of phospholipid/D2O mixtures

The reduction in spectral splitting, or motional narrowing, of the deuterium spectra of D₂O/phos-pholipid mixtures near the main chain melting phase transition was studied for palmitoyloleoylphosphatidylcholine (POPC), palmitoyloleoylphosphatidylethanolamine (POPE) and equimolar mixtures of the two at 10% hydration. For POPC the splitting was about 1700 Hz in both the fluid and gel phases, dropping to zero near the phase transition (as reported previously). For POPE the splitting remained approximately constant above the phase transition. Below the phase transition the spectrum showed a single broad line whose linewidth varied between 100 Hz and 800 Hz. This was interpreted as being due to small domains of water within a weakly hydrated crystal. POPC:POPE (1:1) samples exhibited motional narrowing behaviour similar to that for POPC except that the splitting above the phase transition was approximately twice that below the transition. The relatively broad temperature range (20 K) of the transition is explained using a simple physical model involving lipid fluctuations near the phase transition.Abbreviations NMR Nuclear Magnetic Resonance - PC phosphatidylcholine - PE phosphatidylethanolamine - POPC Palmitoyloleoylphosphatidylcholine - POPE Palmitoyloleoylphosphatidylethanolamine - H_II Inverse hexagonal phase