Regio-specific assignment

Further regio-specific assignments of the observed NMR peaks to the transmembrane a-helices, loops and N- or C-terminus is readily feasible in view of their respective chemical shifts, corresponding to the a-helix form, turned structure, and random coil forms, respectively, with reference to the conformation-dependent displacements of the chemical shifts, to be described in the next section. 

A general feature of dynamic aspect of membrane proteins has been revealed by site-directed NMR studies on bacteriorhodopsin as a typical membrane protein and a variety of mutants at ambient temperature. NMR signals in the spectrum of [3- C] Ala- or [1- C] Val-labelled proteins were assigned regio-specifically with reference to the data of the conformation-dependent chemi-... 

An earlier report by Maruyama et al. described the formation of dimers (439) from the direct irradiation of the acetylquinone (440). In the presence of an electron-donating sensitizer (Rose Bengal) irradiation of the same quinone yields a different dimer assigned structure (441). A further account of the regio- and stereo-specific dimerization of the quinones (442) to yield (443) has been reported. The possibility of the involvement of an enol intermediate was considered. In one example, that of (444), dimerization failed and the cyclobutene derivative (455) was obtained via a Norrish Type II reaction. 

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