these microtubules , which consist of a mixture of 70 % tubulin and 30 % microtubule-associated proteins ( maps ) , undergo a net addition of tubulin at one end of each microtubule ( a end ) and a precisely balanced net loss of tubulin at the opposite end ( d end ) at steady state in vitro .
C0026046
microtubule
C0041348
tubulin