[Activation of Fe2+-induced chemiluminescence in human blood low density lipoproteins by the fluorescent dye C-525].

The effect of the fluorescent dye 2,3,5,6-1H,4H-tetrahydro-9-(2'- benzoimidazolyl)-quinolizin-(9,9a,1-gh)coumarin (C-525) on the chemiluminescence (CL) flash kinetics accompanying Fe(2+)-induced free radical lipid hydroperoxide decomposition in low density lipoproteins (LDL) have been studied. C-525 was found to increase CL flash intensity by a factor of more than 2000 at the concentration of 4 mkM without any influence on the CL kinetics. The mechanism of the CL amplification is apparently energy transfer from the primary excited product of lipid peroxyl radical recombination to fluorescent level of the C-525. A concentration dependencies of CL amplification degree by C-525 on the LDL concentration were revealed to be bell-shaped, so that for 0.01 mg/ml of LDL protein the maximum amplification degree was observed at 4 mkM of C-525, whereas for 0.02 mg/ml of LDL--at 8 mkM. For the elucidation of these effects the properties of C-525 as hydrophobic fluorescent probe have been used. The concentration dependencies of C-525 fluorescence in the LDL suspension were found to be similar to that of CL amplification by C-525. These data pointed to the fact that concentration dependencies of the CL amplification by C-525 was conditioned by its accumulation in a hydrophobic phase of lipoproteins, so that the effective dye concentration was determined by both the amount of C-525 added to the suspension and the concentration of LDL.