by three cycles of assembly and disassembly microtubules could be isolated from the extracellular material which were composed of alpha- and beta-tubulin ( m ( r ) : 55,000 ) , several polypeptides within the m ( r ) range 55,000-82,000 ( presumably tau proteins ) and one protein of an m ( r ) higher than 100,000 .
C0026046
microtubules
C0005290
beta-tubulin