Differences in the isoelectric focusing patterns of serum and cerebrospinal fluid transthyretin.

Transthyretin isolated by polyacrylamide gel electrophoresis from human serum and cerebrospinal fluid, dissociated into its subunits, was subjected to isoelectric focusing in polyacrylamide gels containing 8 mole/L urea. The isoelectric focusing multi-component patterns of serum and cerebrospinal fluid transthyretin differ in a characteristic way, having only one main protein zone in common. Double diffusion immunotest and immunoblotting revealed the immunological identity of serum and cerebrospinal fluid transthyretin and of the main components separated by isoelectric focusing. The different isoelectric focusing zones can be consistently explained when they are ascribed to structurally identical transthyretin subunits associated with different ligands specifically occurring in either serum or cerebrospinal fluid. Only the protein zone located at the same pI in serum and cerebrospinal fluid transthyretin patterns may be assigned to ligand-free subunits. Thus, the typical differences in isoelectric focusing patterns may point to different carrier functions of transthyretin in serum and cerebrospinal fluid.