Emission spectra of melittin

Melittin is an amphipathic peptide component of bee venom which associates with cell membranes, enhances the phospholipase activity of venom and participates in the disruption of cell membranes. This protein has been studied extensively by 

Melittin is an ideal protein to illustrate the effects of structure on the fluorescence spectral properties. Each monomer contains a singly tryptophan residue and no tyrosine residues. The X-ray structure of the tetrameric form shows that the tryptophan residues are buried in a non-polar pocket and are not directly exposed to the aqueous phase. 

The emission spectra of melittin illustrate the effects of solvent exposure on the tryptophan emission (Fig. 7). In the absence of salt, the emission maximum of 360 nm is comparable to that found for NATA in water. In the presence of 2 M NaCl the emission maximum is blue shifted by 12 nm to 348 nm. This shift is a result of shielding of the indole ring from the aqueous phase. Hence, solvent relaxation proceeds to a lesser extent because there is less solvent available for interaction with the fluorophore. 

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Fig. 7. Emission spectra of melittin in the absence (-data are courtesy of N. JoshL... 

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