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A HIGH RESOLUTION FLUORESCENCE DECAY AND DEPOLARIZATION STUDY OF HUMAN PLASMA APOLIPOPROTEINS
Author(s) -
Chang Mary C.,
Fleming Graham R.,
Scanu Angelo M.,
Yang NienchuC
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02736.x
Subject(s) - chemistry , fluorescence , depolarization , tryptophan , rotational correlation time , analytical chemistry (journal) , exponential decay , biophysics , chromatography , biochemistry , molecule , optics , physics , organic chemistry , amino acid , nuclear physics , biology
— Human plasma apolipoprotein A‐I (apoA‐I) and apolipoprotein C‐I (apoC‐I) were investigated by time‐resolved fluorescence decay and depolarization. The tryptophyl fluorescence of apoA‐I undergoes a double‐exponential decay with lifetimes of 1.07 and 3.43 ns which remain unchanged over the range of apoA‐I concentration studied. The time‐resolved fluorescence of both native and denatured forms of apoC‐I exhibits an unusual tryptophyl fluorescence decay that was best fit to a triexponential function with lifetimes at 3.7 ± 0.2, 1.1 ± 0.1 and 0.1 ns at 2°C. The native and denatured forms of apoC‐I had rotational correlation times of 1.42 and 1.19 ns at 20°C respectively. A shorter rotational correlation time associated with the internal tryptophan motions was not observed or resolved. The decay of tryptophyl fluorescence in apoC‐I/DPPC/cholesterol complex at 20°C is also triexponential with lifetimes at 4.94, 1.28 and 0.21 ns, which are longer than those of the uncomplexed forms. Two rotational correlation times of 28.32 and 0.59 ns at 20°C were resolved by fluorescence depolarization measurements. The long rotational time remained constant with temperatures above 30°C. Also, the temperature dependence of the order parameter, S 2 , resembled a lipid phase transition curve with a transition midpoint at 38°C. The tryptophan and thus apoC‐I are found to be affected by the bulk changes in the lipid.