Investigations on the structural perturbations induced by the binding of mercuric chloride to L-glutamate dehydrogenase.

Three mercuric chloride binding sites are identified on l-glutamate dehydrogenase. In the presence of EDTA, the binding of two mercuric chloride molecules per subunit induces the dissociation of the polyhexamers into hexamers. The physical and catalytic properties of this modified hexamer are similar to those of the native enzyme. This induced dissociation of the enzyme is probably the result of an exclusive binding of the mercurial to the free hexamer, and the dissociation velocity does not appear to be rate limited by the binding reaction of the mercurials. The third mercuric chloride binding site is protected by both EDTA and l-glutamate. The binding of HgCl₂ to this site leads to the complete inactivation of the protein. There is no overlap between these modifications of l-glutamate dehydrogenase and the two previously described modifications of the enzyme by mercurial.