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.

• Authors: M T Henzl, R C Hapak, E R Birnbaum
• Journal: Biochimica et biophysica acta (Biochim Biophys Acta) Vol. 872 Issue 1-2 Pg. 16-23 (Jul 25 1986) ISSN: 0006-3002 [Print] Netherlands
• PMID: 3730394 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Calcium-Binding Proteins
• Metals, Rare Earth
• oncomodulin
• Terbium
• Europium
• Magnesium
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Calcium-Binding Proteins (metabolism)
• Europium (metabolism)
• Lasers
• Liver Neoplasms, Experimental (analysis)
• Magnesium (metabolism)
• Male
• Mathematics
• Metals, Rare Earth (metabolism)
• Rats
• Rats, Inbred BUF
• Spectrometry, Fluorescence
• Terbium (metabolism)