two tubulin variants , isolated from chicken brain and erythrocytes and known to have different peptide maps and electrophoretic properties , are demonstrated to exhibit different assembly properties in vitro : 1 ) erythrocyte tubulin assembles with greater efficiency ( lower critical concentration , greater elongation rate ) but exhibits a lower nucleation rate than brain tubulin , and 2 ) erythrocyte tubulin readily forms oligomers whose presence significantly retards the rate of elongation , suggesting that tubulin oligomers may also be important for determining the rate of assembly and the length of microtubules in erythrocytes .
C0041348
tubulin
C0026046
microtubules