99% (By SDS-PAGE). Single band at 55 kDa., When tubulin at a concentration of 1.0 unit/mL (in G-PEM buffer plus 10% glycerol [v/v]) is incubated at 35 °C for 30 minutes an increase in optical density (OD340nm) from 0.0 to 1.0 is observed. This corresponds to a total microtubule (MT) polymer mass of >4.8 mg/mL. The mean length of the microtubule population under these conditions is approximately 10 μm as measured by immunoflourescence microscopy and the average number of MTs per mL is 1.0 x 1012.