Physicochemical and kinetic properties of iodinated yeast 3-phosphoglycerate kinase.

The present studies have established that there is a critical tyrosyl residue in yeast 3-phosphoglycerate kinase. The iodination of this enzyme results in an inactivation following first-order kinetics. The extent of the modification is limited to only one tyrosyl residue. The monoiodotyrosine formation which leads to inactivation of the enzyme does not induce any significant conformational change as evidenced by hydrogen exchange and optical rotatory dispersion. The role of this tyrosine in the action of the yeast 3-phosphoglycerate kinase is studied. An effective protection against inactivation is observed with 3-phosphoglycerate, and the characteristic spectral effect of 3-phosphoglycerate binding cannot be detected in the modified enzyme. It is concluded that the essential tyrosyl residue may play a role in substrate binding.