Microtubules are constituent parts of the mitotic apparatus, cilia, flagella, and elements of the cytoskeleton. They consist principally of 2 soluble proteins, alpha- and beta-tubulin, each of about 55,000 Da. Antibodies against beta Tubulin are useful as loading controls for Western Blotting. However it should be noted that levels of β-Tubulin may not be stable in certain cells. For example, expression of β-Tubulin in adipose tissue is very low and therefore β-Tubulin should not be used as loading control for these tissues.