Anions and particularly sulfate are known to interact with 3-phosphoglycerate kinase and to induce an increase of its catalytic efficiency. The present work affords information on the location of the anionic site and on the conformational change produced by the sulfate binding. We have established that sulfate is able, first, to modify the environment of some critical amino acids (cysteine and arginines) located in the N-terminal half of the protein, second, to induce perturbation of aromatic residues as judged by spectrophotometry, and, third, to slightly decrease the magnitude of the Cotton effect at 233 nm. All these modifications are produced by sulfate concentrations required for the activation of the enzyme. The most striking result consists in a large change in the hydrodynamic properties of the protein upon sulfate interaction as determined by analytical ultracentrifugation studies. Thus, sulfate modifies the shape of the molecular, causing it to become more compact. Furthermore, a study of the binary and ternary complexes between yeast 3-phosphoglycerate kinase and its substrates suggests that such a change of the shape of the molecular only occurs in sulfate-enzyme with or without substrates and in ATP (with or without Mg2+)-3-phosphoglycerate-enzyme complexes.
A high‐molecular‐weight protein has been isolated from hog thyroid gland. This protein, with a molecular weight of 475000 determined by ultracentrifugation and gel filtration, is a complex of two polypeptides with apparent molecular weights of 250000 and 240000. It may be related to filamin‐like proteins by its physicochemical properties and its immunogenic cross‐reactivity towards gizzard filamin antibodies. Furthermore it interacts with F‐actin in a stoichiometry of 1 mol of high‐molecular‐weight protein/∼ 12–14 mol actin monomer allowing microfilament association, as shown by electron microscopy.
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