An electron paramagnetic resonance study of bovine alpha-lactalbumin-metal ion complexes.
An electron paramagnetic resonance study of bovine alpha-lactalbumin-metal ion complexes.
复制标题
牛α-乳清蛋白-金属离子复合物的电子顺磁共振研究。
DOI：
10.1016/0162-0134(86)80048-4
复制
发表时间：
1986
影响因子：
3.9
通讯作者：
Berliner,LJ
中科院分区：
文献类型：
--
作者：
Musci,G;Reed,GH;Berliner,LJ
Abstract α-lactalbumin has at least three distinct cation binding regions: a Ca (II)-Gd (III) site, a Cu (II)-Zn (II) site and a VO 2+ site as observed from electron paramagnetic resonance (EPR) studies of complexes with the bovine protein. Gadolinium, which bound to the calcium site of the protein with a subnanomolar dissociation constant, yielded EPR spectra at 9.5 GHz (X-band) that exhibited features from g= 8 to g= 2. At 35 GHz (Q-band) the central fine structure transition (M s= 1 2→ M s=− 1 2) gave a well-defined powder pattern. The zero-field splitting was large, as reflected in the second-order splitting of the central fine structure transition of about 1 kG. There was also evidence for additional, low affinity binding site (s) for Gd (III). Addition of either Zn (II) or Al (III) did not affect the amplitudes or positions of the bound Gd (III) EPR spectrum. The Cu (II)-α-lactalbumin complex gave a typical axially symmetric spectrum (g¦¦= 2.260, gXXX= 2.056, A¦¦= 171 G) with a partially resolved superhyperfine interaction attributable to at least one directly coordinated nitrogen ligand. Addition of Cu (II) to Gd (III)-α-lactalbumin gave an EPR spectrum that was a superposition of signals from the individual Gd (III)-and Cu (II)-α-LA spectra. The absence of any magnetic interactions in the Gd (III)-Cu (II)-α-lactalbumin species indicated that the two cation sites were more than 10 Å apart. On the other hand, addition of Zn (II) to Cu (II)-α-lactalbumin gave a set of EPR lines due to free or loosely bound Cu (II), confirming that the Cu (II) was displaced by zinc. The EPR spectra for VO 2+-α-lactalbumin at both X-and Q-band were characteristic of an axially symmetric site. The spectral parameters (g¦¦= 1.936, gXXX= 1.977, A¦¦= 174.3× 10− 4 cm− 1, AXXX= 65.1× 10− 4 cm− 1) correlated with those expected for four oxygen ligands in the equatorial plane. Neither Ca (II) nor Zn (II) addition displaced VO 2+ from its binding site, suggesting that it binds to a unique site on the protein.
