ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The luminescent EuIII ion has been used to probe the metal-binding sites of bovine α-lactalbumin (BLA) in D2O. Upon addition of apo-BLA to an EuIII-containing solution, the intrinsic luminescence of the protein is quenched, and the EuIII luminescence is enhanced. Luminescent titrations point to there being at least two different metal-binding sites in the apo-protein. Curve analysis of the high resolution 5D0←7F0 excitation spectra reveals the existence of three different environments for the bonded EuIII ions. Two environments, labelled Ia and Ib, give 5D0←7F0 bands very close in energy; they contain four negatively charged groups and are assigned to one site we identify as the calcium-binding site. Site I is protected from solvent influences and is somewhat rigid, since it displays selectivity towards lanthanide ions. The origin of the two similar environments Ia and Ib could not be determined unambiguously. The third environment is ascribed to a nonspecific metal-binding site in which the EuIII ion is more exposed to the solvent (site II). It is sequentially populated after saturation of site I, and its population is pH-dependent. The affinity constant of EuIII for this site was estimated from the excitation spectra: log K2app = 3.5(1). Assignment of the metal binding sites has been facilitated by comparison with model compounds, [Eu(dota)]- (dota = 1,4,7,10-tetraazacyclododecane N,N′,N″, N‴-tetraacetate), [Eu(dtpa)]2- (dtpa = diethylenetriamine tetraacetate), and [Eu(bsa)] (bsa = bovine serum albumin). The usefulness and limits of the use of curve-analysis procedures to unravel the various components of 5D0←7F0 excitation spectra in biological materials are also discussed.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19940770132
