Comparative measurement by radioimmunoassay of the brain microtubule-associated protein MAP2

The presence of the microtubule-associated protein (MAP2) in the brain of several species has been investigated by SDS-gel electrophoresis and by radioimmunoassay. This assay had a sensitivity of approx. 10 ng and it was capable of measuring the protein either in purified microtubules or in crude brain extracts. As determined with this radioimmunoassay, MAP2 accounted for about 10% of the porcine brain microtubule protein and 1% of the protein from a brain extract. Taking porcine MAP2 as a reference, we have detected polypeptides with the same electrophoretic mobility in brain microtubules from cow, sheep, rat and chicken. Nevertheless, the MAP2 from these species showed a variable degree of immunoreactivity. Bovine MAP2 appeared closely related to the porcine protein whereas the rat antigen showed low cross-reaction and chicken MAP2 appeared immunologically unrelated to porcine MAP2. Our results suggest a higher variability of the MAP2 sequences as compared to that reported by other authors for the brain microtubule protein, tubulin.