CARBON‐13 NUCLEAR MAGNETIC RESONANCE STUDIES ON 13C‐ENRICHED RETINALS EMBEDDED IN BACTERIORHODOPSIN

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Abstract
Abstract— Both [15‐13C] and [14‐13C] all‐trans‐retinals were synthesized. Bacteriorhodopsin containing [14‐13C]retinal as a chromophore, when solubilized with octyl‐β‐D‐glucoside, showed characteristic resonances at 125 and 118 ppm from tetramethyl silane. The former was assigned to the signal from free retinal and the latter from protonated Sehiff base. When the bacteriorhodopsin was denatured in sodium dodecyl sulfate, the signal at 118 ppm disappeared, while the signal at 125 ppm rather increased.In the case of bacteriorhodopsin containing [15‐13C]retinal, when solubilized with Triton X‐100, a characteristic resonance at 169 ppm was distinguishable as a shoulder peak superimposed on the broad signal of carbonyl carbons and it was assigned to the signal from the protonated Sehiff base. The other signal observed at 191 ppm was from free retinal.These results suggested that the Sehiff base of bacteriorhodopsin is protonated in the dark.