We have measured the extended X-ray absorption fine-structure spectra of Zn-concanavalin A and of Zn,Ca-concanavalin A on the high-energy side of the K absorption edge of Zn. Analysis of the spectra shows that, in Zn-concanavalin A, the Zn is hexaco-ordinate with a mean metal-to-ligand distance of 2.06 ± 0.l Å. Formation of Zn,Ca-concanavalin A by binding of Ca2+ at the calcium-specific site is accompanied by a decrease of the co-ordination number of the Zn from six to five with virtually no change in metal-to-ligand distance (2.02 ± 0.1 Å). The geometry of the hexaco-ordinate and pentaco-ordinate complexes and the mechanism of their interconversion are discussed.
|Number of pages||6|
|Journal||Journal of Molecular Biology|
|State||Published - 5 Dec 1979|
Bibliographical noteFunding Information:
Thr help of the staff of the Stanford Sytlchroton Radiation Laboratory (SSRL) is deeply appreciated. The SSRL is support,ed by National Science Foundation grant no. DMR-73. 07692 in co-operationwith the Stanford Linear Accelerator Center and the U.S. Department of Energ-. The research of two of us (E. A. S. and S. M. H.) was slIpported in part by SSF grant no. PCH 76.21849 AOl.