title: Derivative spectroscopy of tryptophan fluorescence used to study conformational transitions in the (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum.
abstract: Second and fourth derivatives have been calculated from the fluorescence emission spectra of N-acetyl tryptophanamide in solvents of varying polarity. It is demonstrated that the otherwise featureless fluorescence emission spectrum can be resolved into a series of discrete bands by the use of the derivative technique. These bands appear to have their origins in the transitions of electrons from the first excited singlet state back to the various vibrational levels of the ground state. The shifting of the fluorescence emission maximum to shorter wavelengths upon decreasing the solvent polarity is shown to be due to changes in the relative contributions of each of the bands combined with smaller changes in the band positions. Derivative spectra have also been obtained from the intrinsic tryptophan fluorescence of the (Ca2+ + Mg2+)-adenosine triphosphatase of sarcoplasmic reticulum membranes. A similar pattern of bands is observed to that found in the model system and is consistent with the majority of the tryptophan residues being located in hydrophobic environments. Addition of calcium ions to the protein results in enhancement of the protein fluorescence accompanied by a small and hitherto unseen blue-shift of the spectrum. The mechanistic implications of this finding are discussed in relation to the calcium transport function of the protein.
mesh_terms: D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D011487:Protein Conformation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013050:Spectrometry, Fluorescence; D014364:Tryptophan
chemical_list: D014364:Tryptophan; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases