AN X-RAY-ABSORPTION SPECTROSCOPY STUDY OF THE INTERACTIONS OF NI2+ WITH YEAST ENOLASE

An x-ray absorption spectroscopy (XAS) study was carried out at pH 7.6 on solutions of Ni2+ and yeast enolase depleted of its physiological cofactor (Mg2+) in the presence or absence of substrate/product, the v ery strongly bound competitive inhibitor 2-phosphonoacetohydroxamate a nd Mg2+. Both ''conformational'' and ''catalytic'' Ni2+ are distorted octahedral in coordination, in agreement with several spectroscopic st udies but in contrast to the coordination in the crystal at pH 6.0. Th e data are consistent with direct coordination of what must be the cat alytic Ni2+ to the phosphate of the substrate, in agreement with some previous data but in disagreement with recent interpretations by other workers. The ligands around the metal ions obtained from the x-ray st ructure give simulated XAS spectra in good agreement with the observed spectra.