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 as1, as2, b, and k casein, supported motility and averaged speeds of 96667 nms. Alpha casein can be purchased as a combination of as1 and as2 and supported gliding motility and average speeds of 94964 nms. Beta casein did not support motility very well and averaged speeds of 870630 nms. Kappa casein supported motility very poorly and we were unable to obtain an average speed. Finally, we observed that mixing alpha, beta, and kappa casein with the proportions found in bovine whole casein supported motility and averaged speeds of 96666 nms.