Determination of cysteine on low-density lipoproteins using the fluorescent probe, 5-iodoacetamidofluoresceine.

Using the fluorescent sulfhydryl probe, 5-iodoacetamidofluoresceine, to label the free sulfhydryl of low-density lipoprotein, the positions of two cysteine residues in apolipoprotein B were located. The tryptic peptides containing the fluorescent probe were isolated by high-performance liquid chromatography systems and sequenced by automatic techniques. The free cysteine residues of apolipoprotein B-100 on low-density lipoprotein are located at positions 3734 and 4190, either or both of which can potentially form a disulfide linkage with apolipoprotein(a) in lipoprotein(a).