Tryptophan exposure in various conformational isomers of bovine prothrombin fragment 1. An acrylamide quenching study

In order to assess the importance of a variety of environmental factors on the structure of bovine prothrombin fragment 1, we have examined acrylamide quenching of fragment 1 intrinsic fluorescence. Tryptophan exposure, determined from Stern-Volmer plots, is heterogeneous with one or more of the three fragment 1 tryptophans being exposed to solvent. In the presence of Ca2+ or Mg2+ even the most accessible tryptophan(s) are relatively buried. Only small differences in tryptophan exposure may exist between fragment 1-Ca2+ and fragment 1-Mg2+ complexes. Lowering pH, on the other hand, results in increased tryptophan exposure. Finally, structural isomers of fragment 1 which exist in the absence of metal ions have identical tryptophan exposure as determined by acrylamide quenching and fluorescence intensity.