Terbium ion binding to hemocyanin |
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Authors: | Beth E. Nelson Susan J. Gan Kenneth G. Strothkamp |
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Affiliation: | Chemistry Department, Bryn Mawr College, Bryn Mawr, Pa. 19010 USA |
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Abstract: | Terbium ion binds to calcium-free hemocyanin at pH 7.0 and 8.9, and promotes the aggregation of hemocyanin subunits, a phenomenon associated with calcium binding. An excitation maximum for the bound terbium at 293 nm and the results of treating the hemocyanin with N-bromosuccinimide indicate that energy transfer from tryptophan to the bound terbium is responsible for the enhancement of terbium fluorescence. At pH 8.9, addition of calcium to hemocyanin containing bound terbium results in only a partial loss of terbium fluorescence, suggesting heterogeneity in the terbium binding sites. Titration of hemocyanin with terbium also indicates multiple binding sites. |
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