TEMPERATURE-DEPENDENCE OF THE PHOSPHORESCENCE LIFETIMES OF HETEROGENEOUS TRYPTOPHAN RESIDUES IN GLOBULAR PROTEINS BETWEEN 293-K AND 77-K

Abstract— The phosphorescence of five globular proteins containing tryptophan residues was observed in deoxygenated neutral ethylene glycol‐phosphate buffer (1:1 by volume) at 293 and 77 K. Their spectral features at 293 K are closely identical to those at 77 K apart from a lack of tyrosine phosphorescence at 293 K. and are independent of the excitation wavelength between 250 and 310 nm. From the present results. it can be concluded that the buried tryptophan residues are the only phosphorescing centers at room temperature. Their phosphorescence lifetimes were measured as a function of temperature in the range from 77 to 293 K. At room temperature, their phosphorescence lifetimes are between about 1 and 500 ms. On the basis of their temperature dependence, the heterogeneous tryptophan environments are discussed in terms of a temperature‐activated nonradiative rate. We suggest that the observation of the phosphorescence characteristics of globular proteins containing tryptophan residues buried in the interior of the protein molecule at room temperature is likely to prove useful in probing the protein structure in solution. Copyright © 1979, Wiley Blackwell. All rights reserved