Bovine brain kinesin is a microtubule-activated ATPase.

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Abstract
Recently, a protein called kinesin was described, which is capable of inducing movement of inert particles along microtubules. To purify this protein from bovine brain, we used the ability of kinesin to bind to taxol-stabilized microtubules in the presence of inorganic tripolyphosphate. The brain kinesin preparation contained one major polypeptide of 135 kDa and four minor polypeptides of 45-70 kDa. The minor polypeptides were eluted from a gel-permeation chromatography column at the same position as the major component. All the polypeptides of the preparation were capable of binding to the microtubules under identical conditions. The kinesin molecule is most probably a complex of these polypeptides. Brain kinesin had a very low ATPase activity (0.06-0.08 mumol X min-1 X mg-1 in 3 mM Mg2+ at pH 6.7). ATPase activity was strongly stimulated by microtubules (Vmax = 4.6 mumol per min per mg of kinesin). Microtubule-activated kinesin ATPase had a Km for ATP between 10 and 12 X 10(-6) M and a Kapp for microtubules (i.e., polymerized tubulin concentration required for a half-maximal activation) of 12-14 X 10(-6) M. Kinesin had a significant ATPase activity even without microtubules if 2 mM Ca2+ was substituted for Mg2+ (Vmax = 1.6 mumol X min-1 X mg-1; Km = 800 X 10(-6) M). Kinesin is therefore a mechanochemical ATPase that is activated by microtubules.