Tryptophan phosphorescence spectra

Differences between the spectra of fluorescence and phosphorescence are immediately obvious. For all tryptophans in proteins the phosphorescence spectrum, even at room temperature, is structured, while the fluorescence emission is not. (Even at low temperatures the fluorescence emission spectrum is usually not structured. The notable exceptions include a-amylase and aldolase, 26 protease, azurin 27,28 and ribonuclease 7, staphylococcal endonuclease, elastase, tobacco mosaic virus coat protein, and Drosophila alcohol dehydrogenase 12. )... 

Figure 3.2 shows the fluorescence and phosphorescence emission spectrum from tobacco mosaic virus coat protein. These spectra are fairly typical of the tryptophan emission spectra observed from proteins at room temperature. 

Tyrosine, like tryptophan, does not exhibit major changes in its luminescence spectrum when incorporated into peptides. Unlike tryptophan. however, there are large reductions in the fluorescence ii ) and phosphorescence quantum ydelds. It has been concluded from model system studies that COO< ) and NH2 groups contribute to tyrosine quenching in polypeptides On the other hand, COOH n ) and NH3 groups 28W may quench tryptophan luminescence but tryptophan is apparently less sensitive to neighboring groups in the polypeptide chain. 

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