Sampling during restoration

Finally, it is worth keeping in mind that the protein may be perturbed reversibly by the conditions of the NMR experiment. For example, a recent study demonstrated that removal of the bulk buffer that typically separates from the sample during magic angle spinning reversibly altered the conformation of the selectivity filter of the KcsA potassium channel addition of buffer to the rotor restored the conformation.101 Based on this observation of a hydration-induced shift in conformation, it seems prudent to maintain high hydration levels for NMR studies of proteins in general. 

We have established that calcium depletion at pH 8.3 in the dark removed the reversibility of pH 8.3 treatment returned to pH 6.3. The unusual epr signal detected in the depleted samples suggests that the OEC was not in the epr silent Si state in the dark. After calcium depletion at lower pH the formation of the Sa state multiline epr signal was not inhibited suggesting that the Si state was still present in the dark in these samples. Both calcium and vanadyl ions restore the normal Si state in the dark as measured by the ability to generate the epr detectable Sa state, and restore reduction during 4 h dark adaptation. 

It is important to avoid saturation of the signal during pulse width calibration. The Bloch equations predict that a delay of 5 1] will be required for complete restoration to the equilibrium state. It is therefore advisable to determine the 1] values an approximate determination may be made quickly by using the inversion-recovery sequence (see next paragraph). The protons of the sample on which the pulse widths are being determined should have relaxation times of less than a second, to avoid unnecessary delays in pulse width calibration. If the sample has protons with longer relaxation times, then it may be advisable to add a small quantity of a relaxation reagent, such as Cr(acac) or Gkl(FOD)3, to induce the nuclei to relax more quickly. 

The type of proteinaceous binder was correctly identified in all model samples. In only one case (S10), the animal glue was additionally identified, although the restorer who prepared these model samples declared that the sample contained only egg binder. It is possible that this sample was contaminated during its preparation or during laboratory treatment. The results indicate that this method does not allow reliable identification of the presence of individual egg yolk and egg white most probably it is caused by the presence of a trace of egg white that is always present in the egg yolk preparations (and vice versa) and can be detected by the highly sensitive PMM method. The identification of individual types of animal glues will never be reliable by MALDI-TOF mass spectrometry because of their similar composition the application of ESI (electrospray ionisation)-MS/MS (Section 6.5) could possibly overcome this problem. Only the fish glue, whose peptide... 

The sample was collected from a decorative frame of the Universal Judgement and, as in Case Study 2, was detached during restoration. It had a completely waterproof surface, due to materials used in a past restoration treatment, preventing any further intervention. In the same sample several organic materials were identified (Figure 11.11) ... 

Copper and nickel are also common contaminants in Si and can often be introduced during annealing treatments. Both of these impurities are extremely rapid diffusers and cannot be retained in electrically active form even by rapid quenching of diffused samples (Weber, 1983). Quite often, complexes involving Cu or Fe impurities are observed by DLTS in heat-treated Si. All of these centers are hole traps, with Cu giving rise to levels at Ev + 0.20 eV, Ev + 0.35 eV and Ev + 0.53 eV, whereas Ni is related to levels at Ev + 0.18 eV, Ev + 0.21 eV and Ev + 0.33 eV. All of these levels are passivated by reaction with atomic hydrogen (Pearton and Tavendale, 1983), and are restored by annealing at 400°C. 

The dependence of the PL intensity and peak position on oxidation temperature for three different PS samples is shown in Fig. 7.20. Oxidation at 600°C destroys the PL, while the initial PL intensity is restored or even increased after oxidation at 900°C. This effect can be understood as a quenching of PL because of a high density of defects generated during the desorption of hydrogen from the internal surface of PS. Electron spin resonance (ESR) investigations show a defect with an isotropic resonance (g= 2.0055) in densities close to 101 cm for oxidation at 600°C [Pel, Me9]. This corresponds to one defect per crystallite, if the crystallite diameter is assumed to be about 5 nm in diameter. 

Fig. 5.—Decay in the a-D-Mannosidase Activity85 of a Partially Purified, Jack-bean Meal Preparation During Incubation at 37° and pH 5, and the Restoration of Activity by Zn2+. [ZnSO., (final concentration 1 mM) was added to a sample of the incubation mixture after 3 hr, and incubation was continued. , Enzyme alone and O, enzyme + 1 mM ZnS04. The results are expressed as a percentage of the activity in the unincubated, enzyme preparation.39]...

Biotinidase activity in blood and plasma samples can decrease, often in an unpredictable manner, during storage at room temperature or at +4°C, but also during prolonged storage at -20°C, whereas no decrease has been observed at -70°C [5, 15, 32, 35]. However, storage at -70°C is not possible in many centres or practises that send samples for biotinidase assay. Addition of a sulphydryl compound to the assay mixture has been shown to restore activity in blood samples stored at room temperature [35]. Using our assay, which includes 0.5 mM DTT in the assay mix-... 

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