A standard procedure in purifying tubulin is to extract the tissue on ice, then add GTP and warm the tissue extract to 37°C. The warmed extract is then centrifuged at a speed insufficient to pellet average sized proteins, but sufficient to pellet large protein complexes. After centrifugation, the supernatant is discarded, and the pellet is redissolved in cold buffer. GTP is again added to the redissolved pellet proteins, and the solution is again warmed for a few minutes. Then centrifugation at the same speed described above is again performed. This process is repeated several times.

1. How would this process result in purification of tubulin?

2. What contaminating proteins would likely co-purify with the tubulin?