Single-band method limitations

The limitations inherent in the 2-DE approach have resulted in significant efforts to develop alternative approaches that do not depend on 2-DE, and in particular avoid the use of IFF with its attendant problems of protein solubility. The simplest approach is the use of one-dimensional SDS-PAGE in conjunction with protein identification by MS/MS, so that several proteins co-migrating in a single band can be identified. However, this method is limited by the complexity of the protein mixture that can be analysed and has been most successfully applied to the study of protein complexes that can be isolated by techniques such as immunoprecipitation (Figeys and Pinto,... 

Fuhs et al.m investigated P p0 Aj in multilayers of Synechocystis PCC 6803 oriented on mylar sheets by transient W-band EPR. They could show an enhanced resolution of structural parameters of the RP in this model system. A problem is the uncertainty of the orientation distribution (width 30 10°). Limitations and possibilities of the method are discussed in this work. The technique is interesting for all systems for which no single crystals are available. 

IETS is spectroscopically similar in resolution to the infrared method except for differences in the pattern of band intensities. Unfortunately, it is limited to samples held at liquid-helium temperatures. However, in the future, in conjunction with scanning tunneling microscopy, it might yield spectra from single adsorbed molecules on particular sites (JO). 

In a pulse radiolysis study of ethylenediamine soon to be published, Anbar and Hart (2) find a conflicting result. These authors report a single broad absorption band with a maximum at 9200 A. The absorption curve continues to fall off with increasing wavelength toward 11,500 A., the sensitivity limit of their detector. In this system the counter-ion is the molecular ion of the solvent, and no alkali metal atom is present. The result raises a serious question about the assignment of the 13,000 A. band to the solvated electron and calls for further study of these systems by the pulse radiolysis method. 

To compare these methods, in Fig. 40 we show (a) EIX vs. J and (b) /Ph vs. E plots for a CVD single crystal thin-film electrode. We see that with increase in illumination intensity J, the open-circuit potential E(X approaches a limit of 0.7 V, which is close to the photocurrent onset potential (0.75 V). [The photocurrent density squared vs. potential dependence for this electrode, although far from linear (unlike that of Fig. 38), by the extrapolation to yph -> 0 gives the potential value of approx. 0.65 V.] It is concluded that, on the whole, methods (i) and (ii) are in a good agreement and can be used in the determination of the flat-band potential. Similar results were obtained with HTHP single crystals. 

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