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INVESTIGATION OF DYNAMICS OF THE HIV1 PROTEASE. B. Ullrich (1), F. Toelgyesi (1), Z. Szeltner (2), L. Polgar (2) and J. Fidy (1) (1) Institute of Biophysics, Semmelweis University of Medicine, Budapest (2) Institute of Enzymology, Biological Research Centre, Hungarian Academy of Sciences, Budapest We studied the effect of inhibitor-binding on the structure of HIV1 protease by its luminescence parameters such as the fluorescence emission spectra, the quenching of fluorescence with acrylamide and the temperature dependence of low temperature phosphorescence. The determination of the quenching constants was realised measuring the intensity and the lifetime of tryptophane fluorescence of the protein. We also investigated the structural changes in the apoenzyme and enzyme-inhibitor complex during denaturation using urea as denaturing agent. The two tryptophanes of the native apoenzyme were found differently accessible to the solvent and their fluorescence is distinguishable based on the bimolecular quenching constants (kq) of the two lifetime components. The binding of the acetyl-pepstatin inhibitor makes the protein structure more compact and stable, the solvent-accessible tryptophane of apoenzyme becomes more covered during the inhibitor-binding, as shown by the decreased quenching constant of the c1 component. The stabilising effect of the inhibitor-binding is also confirmed by the different temperature dependence of phosphorescence in case of the apoenzyme and the enzyme-inhibitor complex, the freedom of motion of the tryptophane residues is decreased in the enzyme-inhibitor complex. This work is supported by Hungarian Grants FEFA 693, 265 and 416. ## Back to the list of abstracts