THE MODE OF ATP-DEPENDENT MICROTUBULE-KINESIN SLIDING IN THE AUXOTONIC CONDITION

Kinesin is a motor protein that converts chemical energy derived from ATP hydrolysis into mechanical work to transport cellular components a long microtubules, We studied the properties of ATP-dependent microtub ule-kinesin sliding with two different in vitro assay systems, In one assay system, a kinesin-coated glass microneedle (elastic coefficient, 1-2.5 pN mu m(-1)) was made to slide along an axoneme, Using this sys tem, we obtained the relationship between the force (=load) on the mic roneedle and the velocity of microneedle-kinesin sliding in the auxoto nic condition, in which the load on the microtubule-kinesin contacts i ncreased as sliding progressed, The force-velocity curve was upwardly convex (maximum velocity V-max, 0.58+/-0.15 mu ms(-1); maximum isometr ic force P-0, 5.0+/-1.6 pN) and was similar to that of in vitro actin- myosin sliding in the auxotonic condition, suggesting that the two mot or protein systems have fundamental kinetic properties in common, In t he other assay system, an axoneme attached to a glass microneedle (ela stic coefficient, 4-5 pN mu m(-1)) was made to slide on a kinesin-coat ed glass surface (V-max, 0.68+/-0.17 mu ms(-1); P-0, 46.1+18.6 pN). Th e change in shape of the axoneme indicated an enormous flexibility of randomly oriented kinesin molecules.