A monoclonal antibody that cross-reacts with phosphorylated epitopes on two microtubule-associated proteins and two neurofilament polypeptides.

A monoclonal antibody is described that was raised against bovine brain microtubule-associated protein (MAP) 1B. Immunoblot analysis revealed that immunoreactivity was abolished by dephosphorylation of the antigen. The antigen/antibody reaction was also directly inhibited by sodium phosphate. In whole brain tissue, MAP 1B was the primary immunoreactive species. However, the antibody was also found to react with MAP 1A as well as with the high and middle molecular weight neurofilament polypeptides. No cross-reaction with MAP 2, which is known to be extensively phosphorylated, other MAPs, or the low molecular weight neurofilament polypeptide was observed. This evidence suggests at least some sequence homology between these different polypeptide components of the neuronal cytoskeleton and points to a common mechanism for their phosphorylation.