Tryptophan Emission from Trypsin and Polymer Films

Abstract

THE sensitivity of the fluorescence and phosphorescence of the aromatic amino-acids to variations in their immediate environment^1–6 provides one of the few tools for probing the interior of proteins in a wide range of conditions. The present studies show that for the interval 200°–300° K the phosphorescence from the tryptophans in the enzyme trypsin more closely resembles that from tryptophan in polyvinyl alcohol films (PVA) than that from tryptophan in aqueous systems. This conclusion is based on comparisons of the wavelengths at which the maxima for fluorescence and phosphorescence are observed as well as the quantum yields for emission in the various systems. Two of the most significant observations leading to this conclusion are that: (a) phosphorescence is observed at room temperature from tryptophan in either PVA or trypsin; and (b) temperature has many similar effects on the phosphorescence from tryptophan in PVA and from trypsin. In the range 77°–170° K, however, the trypsin interior seems to be less “rigid” than either a water or PVA matrix.