Nanosecond motions of the single tryptophan residues in apolipoproteins C-I and C-II: a study by oxygen quenching and fluorescence depolarization.
Rotational freedom of the single tryptophan residue in human plasma apolipoproteins C-I (apo C-I) and C-II (apo C-II) was investigated by oxygen quenching and lifetime-resolved anisotropies. The tryptophan in both apo C-I and C-II was highly accessible to oxygen quenching. The tryptophan residue in both apo C-I and C-II and their sodium dodecyl sulfate (SDS) or dimyristoylphosphatidylcholine (DMPC) complexes displayed significant motional freedom on the nanosecond time scale. Lifetime-resolved anisotropies of tryptophan residues under conditions of oxygen quenching revealed an increase in the amplitude of the segmental motions at 40 degrees C as compared to that at 5 degrees C. It was concluded from these studies that both the apoprotein C-I and C-II are highly flexible molecules, and that the nanosecond motions of the tryptophan residue are sensitive to the fluidity of its environment in both SDS and DMPC complexes.
D053302:Apolipoprotein C-I; D053304:Apolipoprotein C-II; D001056:Apolipoproteins C; D055598:Chemical Phenomena; D002621:Chemistry; D004134:Dimyristoylphosphatidylcholine; D005454:Fluorescence Polarization; D010100:Oxygen; D012399:Rotation; D012967:Sodium Dodecyl Sulfate; D013997:Time Factors; D014364:Tryptophan / Q000032:analysis*
D053302:Apolipoprotein C-I; D053304:Apolipoprotein C-II; D001056:Apolipoproteins C; D012967:Sodium Dodecyl Sulfate; D014364:Tryptophan; D010100:Oxygen; D004134:Dimyristoylphosphatidylcholine