Comparison of different molecular forms of glutamine synthetase from Bacillus brevis bb g1 by fluorescence spectroscopy

Résumé

Glutamine Synthetase in Bacillus brevis Bb G1was purified from alanine grown cells (GSala) and pyruvate grown cells (GSpyr). The emission maximum, life times and quantum yield were found to be 329 nm, 5.8ns & 1.8ns and 0.097 for GSala and 320nm, 5.08ns & 1.3ns and 0.032 for GSpyr respectively. The large wavelength shift in he emission maximum, the significant differences in the shape of the spectrum, the change in fluorescence life times and the considerable differences in the quantum yields of GSala and GSpyr clearly indicated that the conformations of both these forms of the enzyme are significantly different from each other and GSpyr has a more compact structure than GSala. The shorter shifts in the spectrum of fluorescence of GSala / GSpyr compared to free tryptophan and the low quantum yield values of GSala / GSpyr indicated that the majority of the fluorescent tryptophan residues in the enzyme are buried inside the protein in a nonpolar hydrophobic microenvironment. The two life times of GSala / GSpyr indicated that the enzyme contained at least two tryptophan residues that fluoresced in two different environments.