Studies of Polypeptide Structure by Fluorescence Techniques

II. THE EFFECT OF TEMPERATURE AND VISCOSITY ON THE POLARIZATION OF FLUORESCENCE OF SYNTHETIC POLYPEPTIDE-DYE CONJUGATES

From the ¹ From the Laboratory of Chemical Pathology, Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115

Changes in temperature and in viscosity affect dye-poly Glu⁶³Lys³⁷ (No. 3) conjugates in different ways. Variation of temperature in solutions of different initial viscosities (up to 9 centipoise at 10°) shows a constant transition temperature (10°) for the polypeptide above which there is accelerated depolarization; at higher viscosities no such thermal transition occurs. In contrast, the transition to accelerated depolarization cannot be induced by changes of viscosity alone. Changes in viscosity at a series of constant temperatures show separate effects due to the dye moiety and to the polypeptide chain. The plot of (1/p + 1/3) against 1/ shows two distinct relaxation times for the 1-dimethylaminonaphthalenesulfonyl-labeled polymer, and for the fluorescein-labeled polymer it shows a series of straight lines, each of which has a different slope and a slight deviation concave to the 1/ axis at high viscosities. The rotational relaxation time of the polypeptide conjugated with 1-dimethylaminonaphthalenesulfonyl chloride is twice that measured with the fluorescein conjugate in aqueous solution, but not in glycerol solutions.

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