Calcium interaction with bovine thyroglobulin: stoichiometry and structural consequences of calcium binding.
Gel filtration studies show that the thyroglobulin (Tg) molecule (dimer) binds from 18 to 50 Ca2+ ions. At pH 7.5 Tg binds 18 Ca2+ ions with a Kd of 1.3 x 10(-5) M, and 50 Ca2+ ions with a Kd of 5.5 x 10(-4) M. The binding of calcium to bovine thyroglobulin increases the absorption band of iodoamino acid residues at 315 nm. In the presence of Ca2+, the fluorescence intensity of 1-anilino-8-naphthalene sulfonate (ANS) is increased about 5-fold by Tg, with a shift in the fluorescence emission maximum from 505 to 490 nm. Thus, thyroglobulin possesses two classes of calcium binding sites with different affinities. The data reported indicate, also, that Ca2+ binding to Tg increases the hydrophobicity of the surface of the molecule.
Acquaviva
R
R
Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università di Napoli, Italy.
Consiglio
E
E
Di Jeso
B
B
Leonardi
A
A
Pinto
F
F
Salvatore
D
D
Formisano
S
S
D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002850:Chromatography, Gel; D007455:Iodine / Q000502:physiology; D008958:Models, Molecular; D019158:N-Acetylneuraminic Acid; D011487:Protein Conformation; D012794:Sialic Acids / Q000502:physiology; D013056:Spectrophotometry, Ultraviolet; D013954:Thyroglobulin / Q000737:chemistry / Q000378:metabolism*
D000817:Anilino Naphthalenesulfonates; D012794:Sialic Acids; D013954:Thyroglobulin; D007455:Iodine; D019158:N-Acetylneuraminic Acid; D002118:Calcium