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Biophys J, August 2001, p. 1180-1189, Vol. 81, No. 2

Fluorescence Study of Conformational Properties of Melanotropins Labeled with Aminobenzoic Acid

Amando Siuiti Ito,* Eduardo Sérgio de Souza,dagger Simone dos Reis Barbosa,Dagger and Clóvis Ryuichi NakaieDagger

 *Faculdade de Filosofia Ciências e Letras de Ribeirão Preto da Universidade de São Paulo,  dagger Instituto de Física da Universidade de São Paulo, and  Dagger Departamento de Biofisica, Universidade Federal de São Paulo, São Paulo, Brasil

The native hormone alpha -melanocyte-stimulating hormone (alpha -MSH) and its more potent analog [Nle4,D-Phe7]alpha -MSH (NDP-alpha MSH), labeled at the amino terminal with the fluorescent aminobenzoic acid (Abz) isomers, were examined by fluorescence methods. We observed energy transfer between the tryptophan9 residue acting as donor and Abz as acceptor, the transfer being more pronounced to the ortho-form of the acceptor. Within the hypothesis that different peptide conformations coexist in equilibrium during the fluorescence decay, we supposed that the intensity decay was modulated by an acceptor-donor distance distribution function f(r). From the time-resolved fluorescence experimental data, we recovered the distance distribution between Abz and Trp9, using the CONTIN program, within the framework of the Förster resonance energy transfer model. The methodology proved to be useful to provide quantitative information about conformational dynamics of melanotropins and its dependency on the solvent. In aqueous medium, alpha -MSH has a broad Abz-Trp9 distance distribution, reflecting the structural flexibility of the peptide. Three different distance populations could be identified in the labeled analog NDP-alpha MSH in water, indicating distinct conformational states for the synthetic peptide, compared with the native hormone. Measurements in trifluoroethanol resulted in the recovery of two Abz-Trp9 distance populations, both for the native and the analog hormones, reflecting the decrease, induced by the solvent, of the conformational states available to the peptides.

Biophys J, August 2001, p. 1180-1189, Vol. 81, No. 2
© 2001 by the Biophysical Society   0006-3495/01/08/1180/10  $2.00




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Copyright © 2001 by the Biophysical Society.