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A novel calcium binding protein (CaBP) was purified to electrophoretic homogeneity from Dunaliella salina. In theh course of purification experiment, this CaBP was identified as a monomer and its molecular weight was about 21 kD and isoelcetric point (pI) value was about 4.1 using isoelectrofocusing. This CaBP was able to bind Ca^2+ even in the presence of an excess MgCl_2 and KCI both in solution. In the SDS-PAGE, the Ca^2+ -bound form migrates more faster than the Ca^2+ -free form. On the contrary, the Ca^2+ -bound form was slower than the Ca^2+ -free form in the nondenaturing PAGE. This means that the CaBP undergoes conformational change in the Ca^2+ -bound condition. Furthermore, UV absorption spectrum and fluorescence intensity of this CaBP was investigated. UV absorption peak was appeared at about 258 nm and decreased somewhat in Ca^2+ -bound condition. In the measurement of fluorescence, maximum intensity was appeared at 303 nm and decreased in Ca^2+ -bound state, similarly as UV absorption spectrum. These show distinct changes upon Ca^2+ -binding, which indicate of structural and/or dynamic changes largely reminiscent of other members of the EF-hand Ca^2+ -binding protein family.
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