On the atomic or "local" contributions to chemical shifts due to the anisotropy of the diamagnetic susceptibility of the aromatic side chain of amino acids and of the porphyrin ring

Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets

Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.

Interaction of L-tryptophan with alpha-cyclodextrin: studies with calorimetry and proton nuclear magnetic resonance spectroscopy

The interaction of L-tryptophan with alpha-cyclodextrin was investigated in a 0.1 M phosphate buffer at pH 7.4 with a LKB 2277 microcalorimeter, using flow mixed mode at 25 degrees C. The thermodynamic parameters for inclusion complex formation obtained are as follows; DeltaG(0) = - 7.03 kJ/mol (K = 17.0), DeltaH(0) = - 9.50 kJ/mol, DeltaS(0) = - 8.3 J/mol K. The driving force for inclusion complex formation was considered to be mainly van der Waals-London dispersion force, and the contribution of hydrogen bonding was secondary in importance. Also, from the measurements of the proton nuclear magnetic resonance spectra and the model building with Corey-Pauling-Koltum atomic models, the probable structures of the complex, together with conformational change of L-tryptophan by complexation, were determined.

Identification of the barstar binding site of barnase by NMR spectroscopy and hydrogen-deuterium exchange

The extracellular ribonuclease from Bacillus amyloliquifaciens, barnase, forms a tightly-bound one-to-one complex with its intracellular inhibitor barstar. The barstar binding site on barnase was characterized by comparing the differences in the chemical shift and hydrogen-deuterium exchange rates between free and bound barnase. Chemical shift assignments of barnase in the complex with barstar were determined from 3D NOESY-HMQC and TOCSY-HMQC spectra of a complex that had been prepared with uniformly 15N-labelled barnase and unlabelled barstar. Hydrogen exchange rates were obtained from an analysis of a series of [15N]HMQC spectra of a sample prepared in the same manner exchanged into D2O. The largest changes in either chemical shift or hydrogen-deuterium exchange rate are observed for residues located in the active-site and substrate binding loops indicating that barstar inhibits barnase activity by sterically blocking the active site.

Theoretical variation of the H alpha chemical shift in acetyl-glycyl-N-methylamide and oligoglycines with molecular conformation and environment

The sum of the magnetic anisotropy and polarization contributions to the magnetic shielding constants of the alpha protons is calculated as a function of the torsion angles about the NC alpha (phi) and C alpha C' (psi) bonds of the dipeptide. The results show that the polarization or electric field effect is several fold larger than the magnetic anisotropy contribution. The calculated variations are large enough to account for the spread of the values measured for these protons in peptides and proteins. The results obtained for polyglycine alpha helices and antiparallel beta sheets are discussed in relation with molecular conformation and environmental effects on the one hand and experimental data on the other.

Interaction of caffeine with L-tryptophan: study by 1H nuclear magnetic resonance spectroscopy

The interaction of caffeine with L-tryptophan was investigated in aqueous solution adjusted to an ionic strength of 0.20, at pH 6.2, by using 1H NMR spectroscopy. Caffeine interacted with L-tryptophan at a molar ratio of 1:1 by parallel stacking. The thermodynamic parameters obtained for the complexation were as follows: delta G degree = -1.70 kcal/mol at 25 degrees C (K = 17.6 M-1), delta H degree = -3.7 kcal/mol, delta S degree = -6.7 eu. It was found that the driving force for parallel stacking is a combination of electrostatic, polarization, and dispersion interactions, and the contribution of hydrophobic bonding is not large. A possible stacking mode is postulated based on the complexation shifts and pi-electron charge distributions of caffeine and L-tryptophan.