Kinesin was prepared from bovine brain as described previously for studies of translocation. A major component of kinesin, (116 kDa) was shown to undergo specific photocrosslinking with [α-32P]ATP, indicating it was an ATP-binding polypeptide. A low ATPase activity associated with kinesin was stimulated up to 5-fold by microtubules to a specific activity of 14 nmol·min−1·mg−1. N-Ethylmaleimide inhibited both [α-32P]ATP binding to the 116 kDa polypeptide and microtubule-stimulated ATPase activity, suggesting that the 116 kDa polypeptide was the catalytic subunit of kinesin. Though the ATPase activity associated with kinesin is low, it may be sufficient to support motility assuming it is coupled to the velocity of translocation.
