Biochemical studies on carotenoids. Part IX. Interaction of lutein with ovalbumin and other proteins: association and acquisition of novel optical activity.

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Lutein bound to some proteins to form complexes soluble in aqueous solutions. The formation of complexes was accompanied by novel changes in the spectroscopic properties of lutein in the visible wavelength region. The absorption peak with a maximum at 446nm and two sub-peaks at 423nm and 474nm in ethanol coalesced to form a single peak at 384nm without fine structures. This lutein with virtually no optical activity in the visible region in organic solvents showed a circular dichroic spectrum which was roughly point-symmetrical with respect to the wavelength of the maximum in absorption spectrum. These spectroscopic properties indicated that lutein molecules two or more in number form an aggregate with chirality in their mutual arrangement in space. Further addition of lutein led to the formation of red precipitates. The molar ratio of lutein-to-ovalbumin in the soluble complex obtained at a mixing ratio of 0.45 was 8, while that of the precipitate rose from 25 to 35 with a higher mixing ratio. Eighty-five percent of the soluble complex was precipitated when centrifuged at 5200 rpm for 15 hours, and the complex remaining in the supernatant had an apparent molecular weight of about 720, 000. These results indicate that lutein and some proteins interact non-stoichiometrically to form complexes heterogeneous with respect to aggregation number.
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