J. Biol. Chem., Vol. 265, Issue 17, 9694-9700, 06, 1990
Eu3+ luminescence studies of oncomodulin. The origin of the pH- dependent behavior
CL Trevino, WA Palmisano, ER Birnbaum and MT Henzl
Department of Chemistry, New Mexico State University, Las Cruces 88003.
The Eu3+ 7F0----5D0 excitation spectra of parvalbumin and oncomodulin are
pH-dependent. Until now, it had been assumed that both the CD and EF
ion-binding sites shared this property and that deprotonation of water
molecules coordinated to the bound Eu3+ ions might be responsible for the
pH dependence. Results obtained with the site-specific variant of
oncomodulin known as D59E, in which glutamate replaces the aspartate
naturally present at position 59, have necessitated substantial revision of
these ideas. It now appears that the pH-dependent behavior is confined to
the CD site. Moreover, we observe no corresponding change in the number of
O-H oscillators coordinated to the bound Eu3+ ions in the pH range over
which we observe the spectroscopic alteration. It is likely that the
behavior results from deprotonation of one or more carboxyl groups
clustered at the COOH-terminal end of the CD domain.
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