The cerebrospinal fluid transferrin/tau proteins. A study by two-dimensional polyacrylamide gel electrophoresis (2D) and agarose isoelectrofocusing (IEF) followed by double-antibody peroxidase labeling and avidin-biotin amplification.

The cerebrospinal fluid (CSF) transferrin/Tau proteins were studied by two-dimensional polyacrylamide gel electrophoresis (2D) followed by immunoblotting and by agarose isoelectrofocusing (IEF), and subsequent double immunofixation, peroxidase staining and Avidin-Biotin Complex (ABC) amplification. The pattern of the Tau protein was similar but not equal to that of the transferrin (Tf). When a genetic variant of Tf was present in the serum, the same variant was also observed in the corresponding CSF Tf and in the Tau fraction. After neuraminidase treatment, both serum and CSF Tf moved to the Tau position on IEF and 2D. On 2D, no desialized precursors of the Tau proteins were detected, whereas the Tf precursors were always detected. No synthesis of the Tau globulin in the brain can, therefore, be inferred. In CSF not treated with neuraminidase, Tf is the only sialoglycoprotein clearly desialized, showing that the Tau fraction cannot be generated by neuraminidase action at CSF level. In fact, the treatment of serum and CSF proteins with neuraminidase produced a clear shift in the isoelectric mobility of all sialoglycoproteins. We clearly demonstrate that the Tau globulin is the result of neuraminidase activity not located in the CSF compartment. We suggest that Tf could be desialized by the action of neuraminidase at the brain level and then be "washed" into the CSF. Brain utilization of Tf, meeting the brain iron requirement, seems likely.