Protonated form of histidine 238 quenches the fluorescence of tryptophan 241 in subtilisin Novo
- 1 May 1983
- journal article
- research article
- Published by Wiley in International Journal of Peptide and Protein Research
- Vol. 21 (5) , 475-478
- https://doi.org/10.1111/j.1399-3011.1983.tb02674.x
Abstract
The pH dependence of the fluorescence of phenylmethanesulfonyl-subtilisin Novo after excitation at 300 nm is studied. pK values of 5.9 and 10.3 were determined from the titration curve. The major source of indole fluorescence is tryptophan-106. Evidence is presented that the protonated form of histidine-238 quenches the fluorescence of tryptophan-241 in this enzyme. The quenching is explained by a charge-transfer complex formation between the excited indole and imidazole rings which are parallel and quite close to each other in the X-ray model.Keywords
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