Istituto di Biofisica     
Cioni P., Strambini G. B. Dynamical structure of glutamate dehydrogenase as monitored by tryptophan phosphorescece. In: Journal of Molecular Biology, vol. 207 pp. 237 - 247. Elsevier, 1989.
Changes in conformation of glutamate dehydrogenase from beef (liver as a result of interactions with allosteric effectors have been demonstrated from the phosphorescence emission of tryptophan. The triplet state lifetime shows that whereas activators.ADP- and leucine enhance considerably the rigidity of the protein structure surrounding the chromophore, inhibitors GTP, Zn2+ and Ag+ act in an opposite manner increasing the flexibilityof this region of the macromolecule. Such changes in dynamical structure of the protein are confirmed independently for the ADP and GTP complexes by oxygen diffusion studies. Phosphorescence lifetime measurements at various protein concentrations and with the enzyme crosslinked by glutaraldehyde demonstrate that ADP and GTP exert the same effect on the structure of the protein regardless of its degree of polymerization. The in connection between changes in protein structure and regulatory function is strengthened by ethe flndingthat (1) ligands with no regulatory function (Eu3++) do not affect protein structure; (2) pairs of opposite effectors which neutralize each other's_ influence on catalytic activity do restore an apparent native-like structure in the enzyme. Mutual neutralization and the observation that ADP and GTP display maximum) activity atpartial saturation of the binding sites has been interpreted in terms of a model which assumes asymmetry in the hexameric enzyme at the trimer level. Evidence for the existence of conformational heterogeneity among the subunits of the enzyme has been provided.
DOI: 10.1016/0022-2836(89)90453-1
Subject Dynamical structure
Glutamate dehydrogenase
Tryptophans phosphorescence

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