In this study, we report differences in the observed gliding speed of microtubules dependent on the choice of bovine casein used as a surface passivator. We observed differences in both speed and support of microtubules in each of the assays. Whole casein, comprised of α(s1), α(s2), β, and κ casein, supported motility and averaged speeds of 966±7 nm/s. Alpha casein can be purchased as a combina...