ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The effects of pH on the polarization of fluorescence of dyes dissolved in media of high viscosity or conjugated to polypeptides that undergo no structural transitions indicate that DNS is useful for studying pH-dependent molecular transition over the range pH 2.5-14, whereas fluorescein is useful only over the range pH 6-8. Heating and cooling in aqueous solutions cause no change in the polarization of fluorescein or of DNS; therefore, the dyes themselves do not introduce artifacts into heating studies of the dye conjugates. The interaction between fluorescein or DNS and the molecule to which it is conjugated varies and thus may affect the measurements made with the conjugates: the rotational relaxation times of polylysine, of a copolymer of glutamic acid and lysine, and of lysozyme are approximately twice as long when measured with DNS-conjugates as when measured with fluorescein-conjugates. The explanation for this observation is postulated to lie in the tighter binding between fluorescein and the molecule to which it is conjugated, presumably around the point of its covalent attachment, which makes it a better indicator of the behavior of the rotational kinetic unit of the polypeptide chain. The stronger binding of fluorescein is inferred from two lines of evidence: (1) the fluorescent intensity and ultraviolet spectra of a fluorescein-polylysine conjugate are less susceptible to changes in solvent than those of the DNS conjugate, and (2) the net charge of the polypeptide affects the ionization of fluorescein much less than it affects the ionization of DNS. Additional evidence from previous studies corroborates this conclusion. Thus, it is important to establish the relationship between the fluorescent dye and the molecule to which it is conjugated before using the fluorescence data to calculate rotational relaxation times and other molecular parameters.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.1967.360050307
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