J. Biol. Chem., Vol. 263, Issue 22, 10674-10680, 08, 1988
Oncomodulin and parvalbumin. A comparison of their interactions with europium ion
MT Henzl and ER Birnbaum
Department of Chemistry, New Mexico State University, Las Cruces 88003.
The 7F0----5D0 transition of Eu3+ was used to probe the metal-binding
domains of rat oncomodulin and rat parvalbumin. Two distinct differences
between the two proteins were observed. The first relates to the
pH-dependent behavior of their 7F0----5D0 spectra, a phenomenon noted
previously for other paravalbumins. In the case of rat parvalbumin, the
spectral features associated with both metal-binding sites titrate
concomitantly (pK alpha = 8.2); however, in the case of oncomodulin, the
two sites titrate sequentially (pK alpha = 6.3 for the CD site; pK alpha =
8.3 for EF site). The proteins also contrast with regard to their
discrimination for Eu3+ over Ca2+. The CD and EF sites in rat parvalbumin
both display a large preference for Eu3+: (KCa/KEu)CD = 143 +/- 11 and
(KCa/KEu)EF = 191 +/- 30. However, in the case of oncomodulin, although the
EF site of oncomodulin greatly prefers the trivalent lanthanide ion
(KCa/KEu = 300 +/- 80), the CD site exhibits a relatively minor preference
(KCa/KEu = 11 +/- 1).