ACTIVE-SITE BINDING OF METAL IONS IN D-XYLOSE ISOMERASE. H. L. Carrell, Carol E. Afshar, Liat Shimoni-Livny, Jenny P. Glusker, The Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA

The active site of the enzyme D-xylose isomerase contains two divalent metal ions, usually Mg²⁺, Mn²⁺, or Co²⁺.^1,2 We have investigated the structure and characteristics of the metal-free enzyme and the enzyme containing the normally encountered metal ions (Mg²⁺, Mn²⁺, Co²⁺), as well as the effects on the structure of adding divalent cations such as Ni²⁺, Zn²⁺, Pb²⁺, and Ca²⁺. The variation in enzyme activity as a function of added metal ion, and the changes that these metal ions cause in the geometry of the active site of the enzyme will be described. X-ray structural studies have all been carried out at 1.9-1.6 Å resolution. A detailed description of different metal ion environments will be provided. The extent of competition between metal ions for the two sites is revealed by this type of study. The results of our analysis of metal binding will be compared with results from previous NMR studies on some of these systems.³

Supported by grant CA-10925 from National Institutes of Health.

1. Carrell, Rubin, Hurley, and Glusker J. Biol. Chem. 1984, 259, 3230.

2. Carrell, Glusker, Burger, Manfre, Tritsch, and Biellmann Proc. Natl. Acad. Sci. USA 1989, 86, 4440.

3. Sudfeldt, Schaffer, Kagi, Bogumil, Schulz, Wulff, Witzel Eur. J. Biochem. 1990, 193, 863.