INFRARED STUDIES OF INTERACTION BETWEEN METAL-IONS AND CA2-BINDING PROTEINS - MARKER BANDS FOR IDENTIFYING THE TYPES OF COORDINATION OF THESIDE-CHAIN COO- GROUPS TO METAL-IONS IN PIKE PARVALBUMIN (PI=4.10)()

Metal-ligand interactions in the Ca2+-binding sites of pike parvalbumi n (pI = 4.10) have been examined by Fourier-transform infrared spectro scopy. The region of the COO(-)antisymmetric stretch provides useful i nformation on the types of coordination of the COO(-)groups to the met al ions in the Mg2+, Mn2+, and Ca2+-bound forms. In the spectrum of th e Ca2+-bound form, two bands are observed at 1,582 and 1,553 cm(-1), w hereas, in the spectra of the Mg2+ and Mn2+-bound forms, bands are obs erved only in the region around 1,582 cm(-1) and no band is found in t he region around 1,553 cm(-1). The 1,553-cm(-1) band of the Ca2+-bound form reflects the bidentate coordination of the COO(-)groups of both Glu-62 in the CD site and Glu-101 in the EF site to the Ca2+ ions, whi ch has bean made clear by X-ray analysis as a feature of the Ca2+-boun d form. Absence of such a band in the spectrum of the Mn2+-bound form is consistent with the X-ray structure of this form where both of the two COO(-)groups are unidentate. These unidentate COO(-)groups of Glu- 62 and Glu-101 in the Mn2+-bound form seem to give rise to a band at 1 ,577-1,574 cm(-1). The spectrum of the Mg2+-bound form is also consist ent with the 'pseudo-bridging' coordination of the COO(-)group of Glu- 101 reported in the X-ray structure of a form where the Mg(2+)ion occu pies only the EF site, and the same spectrum is further indicative of the 'pseudo-bridging' coordination of the COO- group of Glu-62.