HUMAN PLASMA LOW-DENSITY-LIPOPROTEIN - A FLUORESCENCE STUDY

Hydrophobic nature of human plasma low density lipoprotein surface has been studied by fluorescence spectroscopic method. Enhancement in 8-a nilino-1-naphthalene sulphonate (ANS) fluorescence quantum yield from 0.004 to 0.114 at 470 nm has suggested that the ANS binding sites are fairly low in polarity. LDL has been found to have 77 homogeneous bind ing sites for ANS (K(a) = 2.5 x 10(5)M-1). The binding of an ANS molec ule does not affect the successive binding sites. Variation in tempera ture from 15-degrees to 45-degrees-C did neither alter the number of b inding sites nor association constant. Quenching of protein fluorescen ce (lambda(exc) 286 nm, lambda(ems) 336 nm) indicated the occurrence o f energy transfer in LDL-ANS complex arising from conformational chang es capable of bringing charge acceptor segments near to other ANS site . About 30-fold increase in ANS quantum yield and large shift in the e mission maximum are characteristic features of large hydrophobic envir onment on the surface of IDL particle.