X-RAY-ABSORPTION FINE-STRUCTURE AS A MONITOR OF ZINC COORDINATION SITES DURING OOGENESIS OF XENOPUS-LAEVIS

Citation
Ds. Auld et al., X-RAY-ABSORPTION FINE-STRUCTURE AS A MONITOR OF ZINC COORDINATION SITES DURING OOGENESIS OF XENOPUS-LAEVIS, Proceedings of the National Academy of Sciences of the United Statesof America, 93(8), 1996, pp. 3227-3231
Citations number
26
Categorie Soggetti
Multidisciplinary Sciences
ISSN journal
00278424
Volume
93
Issue
8
Year of publication
1996
Pages
3227 - 3231
Database
ISI
SICI code
0027-8424(1996)93:8<3227:XFAAMO>2.0.ZU;2-Q
Abstract
The x-ray absorption fine structure (XAFS) zinc K-edge steps for intac t stages I,II and V,VI Xenopus laevis oocytes demonstrate that the zin c concentration is about 3 and 1 mM, respectively, However, the chi(k) function for the early stage oocytes differs markedly from that for t he late one, Analysis of the XAFS data for stage I,II oocytes indicate s that zinc is bound to 2.0 +/- 0.5 sulfur atoms at an average coordin ation distance of 2.29 +/- 0.02 Angstrom and 2.0 +/- 0.5 nitrogen or o xygen (N/O) atoms at 2.02 +/- 0.02 Angstrom, In marked contrast, in st age V,VI oocytes, zinc is bound to 4.1 +/- 0.4 N/O atoms at an average distance of 1.98 +/- 0.01 Angstrom. Our previous studies demonstrated that 90% of the zinc in stage VI oocytes is sequestered within yolk p latelets, associated with a single molecule, lipovitellin, the proteol ytically processed product of vitellogenin. XAFS analysis of yolk plat elets, lipovitellin, and vitellogenin demonstrates that zinc is bound to 4.0 +/- 0.5 N/O ligands at an average distance of 1.98 +/- 0.01 Ang strom in each case, identical to that of stage V,VI oocytes, The highe r shell contributions in the Fourier transforms indicate that two of t he N/O zinc ligands are His in both stage V,VI and I,II oocytes, The r esults show that in stage I,II oocytes, there is a high concentration of a zinc protein whose zinc coordination site likely is composed of ( His)(2)(Cys)(2), such as, e,g,, TFIIIA. As the oocytes develop, the pr edominant zinc species becomes one that exhibits the (His)(2)(N/O)(2) zinc site found in lipovitellin, Hence, the ligands to the zinc atoms in intact oocytes and the changes that take place as a function of oog enesis and after their fertilization, during embryogenesis, now can be examined and explored.