UV-LASER-INDUCED CHANGES IN THE INFRARED-SPECTRUM OF CALMODULIN IN THE PRESENCE OF A PHOTOSENSITIVE CA2+ CHELATOR

Nitr-5, a Ca2+ chelator which releases Ca2+ under ultraviolet (UV)-las er irradiation, has been used to obtain direct information on structur al changes induced in the calmodulin molecule upon Ca2+ binding. Infra red spectra have been observed for a mixture of calmodulin and Nitr-5 in D2O solution after UV-laser irradiation, and differences between th ese spectra and the spectrum observed before UV irradiation have been calculated. Spectral changes occur in the amide-I' and COO- antisymmet ric stretching regions upon Ca2+ binding, demonstrating that Ca2+ bind ing causes changes in the protein conformation.