Differences in the protein fluorecence of the two iron(III)-binding sites of ovotransferrin.
1. Changes in the tryptophan fluorescence and the visible absorption spectrum resulting from the combination of apo-ovotransferrin with Fe3+, F,E2+, Cu2+, Zn2+, Mn2+, and Cd2+were measured. 2. As expected for a radiationless transfer of electronic excitation energy, only the ions Fe3+, Fe2+and Cu2+, which gave complexes with large extinctions between 300 and 370nm, resulted in large decreases in trytophan fluorescence. 3. The decrease in protein fluorescence was non-linear with increasing occupancy of the Fe3+ -and Cu2+ - binding sites. The decrease in fluorescence on binding of Fe3+ was biphasic and showed that the two metal-binding sites were being occupied sequentially at pH7.4-8.4. The first site reacted with Fe3+ instantaneously, the second was occupied over a minute. 5. The nonidentity of the two sites was also demonstrated by the preparation of a stable hybrid containing both Cu2+ and Zn2+.h Cu2+ and Zn2+
D001665:Binding Sites; D002104:Cadmium; D002807:Chondroitin / Q000378:metabolism; D003207:Conalbumin; D003300:Copper; D004187:Disaccharides; D004527:Egg Proteins; D005453:Fluorescence; D007501:Iron; D008345:Manganese; D010206:Papain
D004187:Disaccharides; D004527:Egg Proteins; D002104:Cadmium; D003207:Conalbumin; D008345:Manganese; D003300:Copper; D002807:Chondroitin; D007501:Iron; D010206:Papain