Chromatographic and spectroscopic analysis of phycoerythrin 545 and its subunits
Tóm tắt
Phycoerythrin 545 is a light-harvesting biliprotein isolated from the cryptomonad Rhodomonas lens. Although the absorption spectrum of the native protein suggests that this protein has only phycoerythrobilins for its chromophores, the denaturated protein shows a small near ultraviolet absorption band with a maximum at 333 nm which is not present in phycoerythrobilin. Two methods were employed to separate the α and β subunits of this protein: chromatography with Sephacryl S-200 in acidic urea or centrifugation in a sucrose density gradient at pH 3.0. The chromatography experiments yielded two bands, which were shown to be pure α or β subunits by sodium dodecyl sulfate gel electrophoresis. The absorption spectrum of β showed only phycoerythrobilins, but the spectrum of α was not like that of any known bilin chromophore. Its absorption spectrum could be constructed by a combination of phycoerythrobilin and cryptoviolin. The β subunit separated on the sucrose density gradient was highly aggregated. Circular dichroism and fluorescence polarization spectroscopy indicated that this aggregated β subunit has chromophores in atypical environments. Comparison of the absorption, spectra of native and denatured phycoerythrin 545 suggests that chromophores in the native state are held by the protein in a more linear confirmation.
Tài liệu tham khảo
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