Study of the dynamic contacts of macromolecules according to the kinetics of isomerization of a fluorescent label sensitized with a dye in the triplet state

A new method is proposed for recording the dynamic contacts of macromolecules based on study of the kinetics of the photochromic reaction sensitized by triplet-triplet energy transfer between labels (sensitizer and photochrome) bound to the macromolecules studied. The use of the method is demonstrated in relation to study of a model system. The authors studied the kinetics of erythrosin-sensitized cis-trans isomerization of 4-acetoamido-4-iso-thiocyanostilbene disulphonic acid (I) in aqueous solution and also the kinetics of the interaction of I and erythrosin isothiocyanate bound to the molecules of chymotrypsinogen. It was established that the lowest possible recorded frequency of the collisions of the labels is limited by the photodegradation of the sensitizer and amounts to 1 sec^-1.