Thermal Modification of Structure of Tropomyosin
I. Changes in the Intensity and Polarization of the Intrinsic Fluorescence (Tyrosine)
1972 年 71 巻 4 号 p. 597-605
詳細
1972 年 71 巻 4 号 p. 597-605
Changes in the intensity and the polarization of intrinsic fluorescence (tyrosine) of rabbit skeletal tropomyosin were examined as a function of temperature. An anoma-lous thermal quenching was observed at around 34°C in neural salt solution. This was independent of the degree of polymerization of tropomyosin. At the same tem-perature, another type of anomalous behavior of the fluorescence intensity (increase) was observed both in 5M urea where most of the α-helical structure was lost, and at pH 2 where the α-helical structure of the protein was very stable. These results suggested the precence of a small non-helical structure in tropomyosin. Judging from a polarization study, the tyrosine side-chain groups of tropomyosin seemed to be tightly incorporated in the α-helical structure in neutral salt solution. When the temperature was raised an abrupt depolarization was observed at 34°C and at 54°C. The latter corresponded to thermal melting of the α-helix of the protein. Isothermal measurements showed that the abrupt depolarization at 34°C was due to an enhanced thermal activation of the rotation of tyrosine residues. The fraction of the activated residue was estimated to be about 20% of total tyrosine residues.
