PHOTOCHROMIC POLYPEPTIDES - ACCELERATION OF ALPHA-HELIX TO COIL TRANSFORMATION IN LIGHT-ADAPTED POLY(L-SPIROPYRAN GLUTAMATES) BY SUBSTITUENT EFFECTS

The kinetics of the coil to a-helical transformation was studied in li ght adapted hexafuoroisopropanol solutions of spiropyran covalently at tached to poly(l-glutamates), The dark adapted polypeptide had a coil conformation and light adaptation led to ring closure of the merocyani ne form with simultaneous conversion into a-helix. By suitable substit ution on the pyran ring of the spiropyran, it is possible to accelerat e the conformational changes oil the polypeptide hack bone by two orde rs of magnitude. Half lifes of the order of 90 seconds were obtained f or reversible conformational changes. It is interesting to note that t he half lifes for the peptide bound spiropyran photochromic reaction a nd those of helical to coil transition for different substituents, fol low the relative rates of the decoloration reaction of the unbound dye s in solution.