A subnanosecond-pulse fluorometric study of the CA2+ and MG2+ induced conformational changes on S-100a protein

The fluorescence parameters of the single tryptophan residue (Trp 90 alpha) in S-100a (alpha beta) protein have been studied by steady state fluorimetry and by subnanosecond fluorescence decays excited by pulsed-picosecond laser system. At pHs 7.1 and 8.5, double exponential decays were consistently observed. At both pHs, Ca2+ and to a less extent Mg2+ ions proved to modify the percentage contribution of the two decaying species. The interest of the finding is discussed.