Increasing masses of pure bovine brain tubulin were loaded in a 7.5% resolving layer and 6% stacking layer. The pH of resolving and stacking buffers were maintained at 9.8 and 6.8, respectively. The gel was run at 120 V for 1.5 hrs in a running buffer containing 0.1% SDS. Molecular weight markers are shown in lane 1. The mass of tubulin in lane 2 to lane 10 was 8 µg, 12 µg, 16 µg, 20 µg, 24 µg, 28 µg, 32 µg, 36 µg, and 40 µg, respectively.