title: Lanthanide-binding properties of rat oncomodulin.
abstract: Oncomodulin, the parvalbumin-like calcium-binding protein frequently expressed in tumor tissue, was isolated from Morris hepatoma 5123tc and studied using the luminescent lanthanide ions, Eu3+ and Tb3+. Titrations of the apoprotein - whether monitored by indirect excitation of bound Tb3+, by direct laser excitation of bound Eu3+, or by quenching of the intrinsic tyrosine fluorescence - all indicated the presence of two high-affinity binding sites for lanthanide ions, as in parvalbumin. Moreover, the appearance of the Eu3+ 7F0----5D0 excitation spectrum of Eu2-oncomodulin was found to be highly pH-dependent, as previously observed with parvalbumin. At pH 5.0, it consists of a single peak centered at 5796 A, having a linewidth of approximately 6 A. At higher pH values, this spectrum is replaced by a broader, more symmetric peak at 5782 A. Oncomodulin, however, was found to differ from parvalbumin in at least one important respect: In contrast to the muscle-associated protein, the affinities of the CD site in oncomodulation for Tb3+ and Ca2+ were found to be rather similar, with KCa/KTb approximately equal to 11 +/- 2.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D005063:Europium / Q000378:metabolism; D007834:Lasers; D008114:Liver Neoplasms, Experimental / Q000032:analysis; D008274:Magnesium / Q000378:metabolism; D008297:Male; D008433:Mathematics; D008674:Metals, Rare Earth / Q000378:metabolism*; D051381:Rats; D011915:Rats, Inbred BUF; D013050:Spectrometry, Fluorescence; D013725:Terbium / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D008674:Metals, Rare Earth; C034733:oncomodulin; D013725:Terbium; D005063:Europium; D008274:Magnesium; D002118:Calcium