Characterization of the mobility of various chemical groups in the purple membrane of Halobacterium halobium by 13C, 31P and 2H solid state NMR

Lyophilized purple membrane sheets have been investigated by C-13- and P-31-cross polarization/magic angle spinning NMR spectroscopy. The high-resolution C-13 spectrum and its non-quaternary suppression version indicate fast protein side-chain motions but a rigid backbone structure on a time scale of roughly less than 0.001 to 0.01 s. Three components of exchangeable hydrogen have been detected by deuterium NMR. The mean exchange time of the peptide hydrogens must be longer than 1 microsecond. The medium component is attributed to mobile side-chains. In addition a narrow line has been observed which is assigned to the residual hydration water.

NMR field-cycling relaxation spectroscopy of bovine serum albumin, muscle tissue, Micrococcus luteus and yeast. 14N1H-quadrupole dips

The frequency dependence of the proton spin lattice relaxation time of bovine serum albumin, muscle tissue, Micrococcus luteus and yeast has been measured by the aid of the field-cycling technique. In all systems 14N1H-quadrupole dips have been observed. The conclusion is that amide groups are the dominating relaxation centers up to approx. 10(7) Hz. This finding can be understood by the fact that protein backbone fluctuations and, if possible, tumbling of the whole molecule rather than side group motions are the relevant mechanisms in this frequency range. A proton relaxation scheme for cells and tissue is presented.

Solvation of oxygen in lecithin bilayers

The solubility of oxygen in dipalmitoyllecithin (DPL) and paraffinc C19 has been investigated by measurement of the enhanced proton relaxation rates under the influence of oxygen pressure. The paraffin shows a noticeable effect in the rotator phase, but not so in the crystalline phase. tin contrast to paraffins, both phases of DPL-bilayers dissolve oxygen, but the solubility in the liquid-crystalline phase is greater than in the crystalline state by a factor approximately equal to 3. Furthermore, the experiments indicate a distribution of electron relaxation times in the crystalline phase in contrast to the liquid-crystalline phase. A possible explanation of this behaviour is a multiphase structure of the "crystalline' lamellae. The biological relevance of thbse results could be a triggering of the gas-transport by the alveolar lining of lungs, if cyclic phase transitions occur during the breathing-cycle.

Nuclear magnetic relaxation spectroscopy in solutions of bovine hemoglobin

The longitudinal proton relaxation time T1 of aqueous solutions of bovine ferrihemoglobin and carboxilated hemoglobin was measured in the Larmor frequency range 3·103 Hz to 1,2·108 Hz. The dispersion curves are explained by diamagnetic and electron paramagnetic relaxation mechanisms. An efficient direct dipolar coupling between the paramagnetic heme-groups and the water protons in ferrihemoglobin solutions can be excluded. The flat dispersion behaviour of the diamagnetic contribution suggests a broad distribution of molecular motions i. e. a certain flexibility of the hemoglobin molecule.

Zur Deutung der kernmagnetischen Relaxation in Proteinlösungen

Measurements of longitudinal and transversal proton relaxation times in both H2O and mixed H2O/D2O protein solutions show a low-frequency as well as a high-frequency dispersion of the longitudinal relaxation time and a nonexponential two-phase transversal relaxation. These results are discussed qualitatively in terms of “rigid” and “mobile” relaxation centers within the protein molecules.